build: correctly detect clang version

Use the "Apple LLVM" version number since the banner has changed in
newer versions of Mac OS X, resulting in the obsolete assembler path
being used to compile OpenSSL.

PR-URL: #5553
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

Author: Stefan Budeanu

configure

@@ -441,7 +441,7 @@ def try_check_compiler(cc, lang):
 # Commands and regular expressions to obtain its version number are taken from
 # https://github.com/openssl/openssl/blob/OpenSSL_1_0_2-stable/crypto/sha/asm/sha512-x86_64.pl#L112-L129
 #
-def get_llvm_version(cc):
+def get_version_helper(cc, regexp):
   try:
     proc = subprocess.Popen(shlex.split(cc) + ['-v'], stdin=subprocess.PIPE,
                             stderr=subprocess.PIPE, stdout=subprocess.PIPE)
@@ -454,14 +454,20 @@ def get_llvm_version(cc):
         '''
     sys.exit()
 
-  match = re.search(r"(^clang version|based on LLVM) ([3-9]\.[0-9]+)",
-                    proc.communicate()[1])
+  match = re.search(regexp, proc.communicate()[1])
 
   if match: