Code review + tweaks to AMD's AOCL 2.0 PR (#349).

Details:
- NOTE: This is a merge commit of 'master' of git://github.com/amd/blis
  into 'amd-master' of flame/blis.
- Fixed a bug in the downstream value of BLIS_NUM_ARCHS, which was
  inadvertantly not incremented when the Zen2 subconfiguration was
  added.
- In bli_gemm_front(), added a missing conditional constraint around the
  call to bli_gemm_small() that ensures that the computation precision
  of C matches the storage precision of C.
- In bli_syrk_front(), reorganized and relocated the notrans/trans logic
  that existed around the call to bli_syrk_small() into bli_syrk_small()
  to minimize the calling code footprint and also to bring that code
  into stylistic harmony with similar code in bli_gemm_front() and
  bli_trsm_front(). Also, replaced direct accessing of obj_t fields with
  proper accessor static functions (e.g. 'a->dim[0]' becomes
  'bli_obj_length( a )').
- Added #ifdef BLIS_ENABLE_SMALL_MATRIX guard around prototypes for
  bli_gemm_small(), bli_syrk_small(), and bli_trsm_small(). This is
  strictly speaking unnecessary, but it serves as a useful visual cue to
  those who may be reading the files.
- Removed cpp macro-protected small matrix debugging code from
  bli_trsm_front.c.
- Added a GCC_OT_9_1_0 variable to build/config.mk.in to facilitate gcc
  version check for availability of -march=znver2, and added appropriate
  support to configure script.
- Cleanups to compiler flags common to recent AMD microarchitectures in
  config/zen/amd_config.mk, including: removal of -march=znver1 et al.
  from CKVECFLAGS (since the -march flag is added within make_defs.mk);
  setting CRVECFLAGS similarly to CKVECFLAGS.
- Cleanups to config/zen/bli_cntx_init_zen.c.
- Cleanups, added comments to config/zen/make_defs.mk.
- Cleanups to config/zen2/make_defs.mk, including making use of newly-
  added GCC_OT_9_1_0 and existing GCC_OT_6_1_0 to choose the correct
  set of compiler flags based on the version of gcc being used.
- Reverted downstream changes to test/test_gemm.c.
- Various whitespace/comment changes.

sandbox/ref99/blx_gemm_front.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2017, Advanced Micro Devices, Inc.
+   Copyright (C) 2017 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/blx_gemm_int.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/cntl/blx_gemm_cntl.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/oapi/bli_gemmnat.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2017, Advanced Micro Devices, Inc.
+   Copyright (C) 2017 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/blx_gemm_blk_var1.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/blx_gemm_blk_var2.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/blx_gemm_ker_var2.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/blx_gemm_var.h

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/other/blx_gemm_ker_var2rr.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are

sandbox/ref99/vars/other/blx_gemm_ker_var2sl.c

@@ -5,7 +5,7 @@
    libraries.
 
    Copyright (C) 2014, The University of Texas at Austin
-   Copyright (C) 2018, Advanced Micro Devices, Inc.
+   Copyright (C) 2018 - 2019, Advanced Micro Devices, Inc.
 
    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions are