Re-enable and fix fb93d24.

Details:
- Re-enabled the changes made in fb93d24.
- Defined BLIS_ENABLE_SYSTEM in bli_arch.c, bli_cpuid.c, and bli_env.c,
  all of which needed the definition (in addition to config_detect.c) in
  order for the configure-time hardware detection binary to be compiled
  properly. Thanks to Minh Quan Ho for helping identify these additional
  files as needing to be updated.
- Added additional comments to all four source files, most notably to
  prompt the reader to remember to update all of the files when updating
  any of the files. Also made the cpp code in each of the files as
  consistent/similar as possible.
- Refer to issues #532 and PR #546 for more history.

build/detect/config/config_detect.c

@@ -33,12 +33,39 @@
 
 */
 
-#define BLIS_INLINE static
-#define BLIS_EXPORT_BLIS
-#include "bli_system.h"
-#include "bli_type_defs.h"
-#include "bli_arch.h"
-#include "bli_cpuid.h"
+// NOTE: This file will likely only ever get compiled as part of the BLIS
+// configure script, and therefore BLIS_CONFIGURETIME_CPUID is guaranteed to
+// be #defined. However, we preserve the cpp conditional for consistency with
+// the other three files mentioned above.
+#ifdef BLIS_CONFIGURETIME_CPUID
+
+  // NOTE: If you need to make any changes to this cpp branch, it's probably
+  // the case that you also need to modify bli_arch.c, bli_cpuid.c, and
+  // bli_env.c. Don't forget to update these other files as needed!
+
+  // The BLIS_ENABLE_SYSTEM macro must be defined so that the correct cpp
+  // branch in bli_system.h is processed. (This macro is normally defined in
+  // bli_config.h.)
+  #define BLIS_ENABLE_SYSTEM
+
+  // Use C-style static inline functions for any static inline functions that
+  // happen to be defined by the headers below. (This macro is normally defined
+  // in bli_config_macro_defs.h.)
+  #define BLIS_INLINE static
+
+  // Since we're not building a shared library, we can forgo the use of the
+  // BLIS_EXPORT_BLIS annotations by #defining them to be nothing. (This macro
+  // is normally defined in bli_config_macro_defs.h.)
+  #define BLIS_EXPORT_BLIS
+
+  #include "bli_system.h"
+  #include "bli_type_defs.h"
+  #include "bli_arch.h"
+  #include "bli_cpuid.h"
+  //#include "bli_env.h"
+#else
+  #include "blis.h"
+#endif
 
 int main( int argc, char** argv )
 {

frame/base/bli_arch.c

@@ -34,8 +34,26 @@
 */
 
 #ifdef BLIS_CONFIGURETIME_CPUID
+
+  // NOTE: If you need to make any changes to this cpp branch, it's probably
+  // the case that you also need to modify bli_arch.c, bli_cpuid.c, and
+  // bli_env.c. Don't forget to update these other files as needed!
+
+  // The BLIS_ENABLE_SYSTEM macro must be defined so that the correct cpp
+  // branch in bli_system.h is processed. (This macro is normally defined in
+  // bli_config.h.)
+  #define BLIS_ENABLE_SYSTEM
+
+  // Use C-style static inline functions for any static inline functions that
+  // happen to be defined by the headers below. (This macro is normally defined
+  // in bli_config_macro_defs.h.)
   #define BLIS_INLINE static
+
+  // Since we're not building a shared library, we can forgo the use of the
+  // BLIS_EXPORT_BLIS annotations by #defining them to be nothing. (This macro
+  // is normally defined in bli_config_macro_defs.h.)
   #define BLIS_EXPORT_BLIS
+
   #include "bli_system.h"
   #include "bli_type_defs.h"
   #include "bli_arch.h"

frame/base/bli_cpuid.c

@@ -47,12 +47,31 @@
 #endif
 
 #ifdef BLIS_CONFIGURETIME_CPUID
+
+  // NOTE: If you need to make any changes to this cpp branch, it's probably
+  // the case that you also need to modify bli_arch.c, bli_cpuid.c, and
+  // bli_env.c. Don't forget to update these other files as needed!
+
+  // The BLIS_ENABLE_SYSTEM macro must be defined so that the correct cpp
+  // branch in bli_system.h is processed. (This macro is normally defined in
+  // bli_config.h.)
+  #define BLIS_ENABLE_SYSTEM
+
+  // Use C-style static inline functions for any static inline functions that
+  // happen to be defined by the headers below. (This macro is normally defined
+  // in bli_config_macro_defs.h.)
   #define BLIS_INLINE static
+
+  // Since we're not building a shared library, we can forgo the use of the
+  // BLIS_EXPORT_BLIS annotations by #defining them to be nothing. (This macro
+  // is normally defined in bli_config_macro_defs.h.)
   #define BLIS_EXPORT_BLIS
+
   #include "bli_system.h"
   #include "bli_type_defs.h"
-  #include "bli_cpuid.h"
   #include "bli_arch.h"
+  #include "bli_cpuid.h"
+  //#include "bli_env.h"
 #else
   #include "blis.h"
 #endif

frame/base/bli_env.c

@@ -34,10 +34,30 @@
 */
 
 #ifdef BLIS_CONFIGURETIME_CPUID
+
+  // NOTE: If you need to make any changes to this cpp branch, it's probably
+  // the case that you also need to modify bli_arch.c, bli_cpuid.c, and
+  // bli_env.c. Don't forget to update these other files as needed!
+
+  // The BLIS_ENABLE_SYSTEM macro must be defined so that the correct cpp
+  // branch in bli_system.h is processed. (This macro is normally defined in
+  // bli_config.h.)
+  #define BLIS_ENABLE_SYSTEM
+
+  // Use C-style static inline functions for any static inline functions that
+  // happen to be defined by the headers below. (This macro is normally defined
+  // in bli_config_macro_defs.h.)
   #define BLIS_INLINE static
+
+  // Since we're not building a shared library, we can forgo the use of the
+  // BLIS_EXPORT_BLIS annotations by #defining them to be nothing. (This macro
+  // is normally defined in bli_config_macro_defs.h.)
   #define BLIS_EXPORT_BLIS
+
   #include "bli_system.h"
   #include "bli_type_defs.h"
+  //#include "bli_arch.h"
+  //#include "bli_cpuid.h"
   #include "bli_env.h"
 #else
   #include "blis.h"

frame/include/bli_system.h

@@ -70,7 +70,7 @@
 #endif
 
 // Determine the target operating system.
-//#if defined(BLIS_ENABLE_SYSTEM)
+#if defined(BLIS_ENABLE_SYSTEM)
   #if defined(_WIN32) || defined(__CYGWIN__)
     #define BLIS_OS_WINDOWS 1
   #elif defined(__gnu_hurd__)
@@ -94,9 +94,9 @@
   #else
     #error "Cannot determine operating system"
   #endif
-//#else // #if defined(BLIS_DISABLE_SYSTEM)
-//  #define BLIS_OS_NONE
-//#endif
+#else // #if defined(BLIS_DISABLE_SYSTEM)
+  #define BLIS_OS_NONE
+#endif
 
 // A few changes that may be necessary in Windows environments.
 #if BLIS_OS_WINDOWS

frame/include/blis.h

@@ -48,6 +48,15 @@ extern "C" {
 // NOTE: PLEASE DON'T CHANGE THE ORDER IN WHICH HEADERS ARE INCLUDED UNLESS
 // YOU ARE SURE THAT IT DOESN'T BREAK INTER-HEADER MACRO DEPENDENCIES.
 
+// -- configure definitions --
+
+// NOTE: bli_config.h header must be included before any BLIS header.
+// It is bootstrapped by ./configure and does not depend on later
+// headers. Moreover, these configuration variables are necessary to change
+// some default behaviors (e.g. disable OS-detection in bli_system.h in case
+// of --disable-system).
+#include "bli_config.h"
+
 // -- System and language-related headers --
 
 // NOTE: bli_system.h header must be included before bli_config_macro_defs.h.
@@ -55,9 +64,8 @@ extern "C" {
 #include "bli_lang_defs.h"
 
 
-// -- configure definitions --
+// -- configure default definitions --
 
-#include "bli_config.h"
 #include "bli_config_macro_defs.h"