Add #line directives to flattened blis.h. (#643)

Details:
- Modified flatten-headers.py so that #line directives are inserted into
  the flattened blis.h file. This facilitates easier debugging when
  something is amiss in the flattened blis.h because the compiler will
  be able to refer to the line number within the original constituent
  header file (which is where the fix would go) rather than the line
  number within the flattened header (which is not as helpful).

build/flatten-headers.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python
 #
-#  BLIS    
+#  BLIS
 #  An object-based framework for developing high-performance BLAS-like
 #  libraries.
 #
@@ -215,9 +215,19 @@ def flatten_header( inputfile, header_dirpaths, cursp ):
 	# Open the input file to process.
 	ifile = open( inputfile, "r" )
 
+	# A counter to track the line number being parsed within the current file.
+	# This counter, when selectively encoded into the flattened header via #line
+	# directives, facilitates easier debugging. (When the compiler finds an
+	# issue, it will be able to refer to the line number within the constituent
+	# header file rather than the flattened one.)
+	lineno = 0
+
 	# Iterate over the lines in the file.
 	while True:
 
+		# Increment the line number.
+		lineno += 1
+
 		# Read a line in the file.
 		line = ifile.readline()
 
@@ -268,12 +278,14 @@ def flatten_header( inputfile, header_dirpaths, cursp ):
 
 				# Mark the beginning of the header being inserted.
 				ostring += "%s%s%c" % ( beginstr, header, '\n' )
+				ostring += "#line %d \"%s\"%c\n" % ( 1, header_path, '\n' )
 
 				# Recurse on the header, accumulating the string.
 				ostring += flatten_header( header_path, header_dirpaths, cursp + "  " )
 
 				# Mark the end of the header being inserted.
 				ostring += "%s%s%c" % ( endstr, header, '\n' )
+				ostring += "#line %d \"%s\"%c\n" % ( lineno+1, inputfile, '\n' )
 
 				echov2( "%sheader file '%s' fully processed." \
 				        % ( cursp, header_path ) )
@@ -300,7 +312,7 @@ def flatten_header( inputfile, header_dirpaths, cursp ):
 		# endif
 
 	# endwhile
-	
+
 	# Close the input file.
 	ifile.close()
 
@@ -330,7 +342,6 @@ def find_header_dirs( dirpath ):
 	#endfor
 
 	return header_dirpaths
-	
 
 # ------------------------------------------------------------------------------