build: rework -fvisibility=hidden detection

Make the gcc_version macro conform with what node.js and v8 use. Important
because node.js's common.gypi is going to export it soon.

build/gcc_version.py

-#!/usr/bin/env python
-
-import os
-import re
-import subprocess
-import sys
-
-
-def DoMain(*args):
-  cc = os.environ.get('CC', 'gcc')
-  stdin, stderr = os.pipe()
-  subprocess.call([cc, '-v'], stderr=stderr)
-  output = os.read(stdin, 4096)
-  match = re.search("\ngcc version (\d+\.\d+\.\d+)", output)
-  if match:
-    print(match.group(1))
-
-
-if __name__ == '__main__':
-  DoMain(*sys.argv)

common.gypi

@@ -6,6 +6,8 @@
     'library%': 'static_library',    # allow override to 'shared_library' for DLL/.so builds
     'component%': 'static_library',  # NB. these names match with what V8 expects
     'msvs_multi_core_compile': '0',  # we do enable multicore compiles, but not using the V8 way
+    'gcc_version%': 'unknown',
+    'clang%': 0,
   },
 
   'target_defaults': {
@@ -117,9 +119,6 @@
         ],
       }],
       [ 'OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="solaris"', {
-        'variables': {
-          'gcc_version%': '<!(python build/gcc_version.py)>)',
-        },
         'cflags': [ '-Wall' ],
         'cflags_cc': [ '-fno-rtti', '-fno-exceptions' ],
         'conditions': [
@@ -137,7 +136,7 @@
             'cflags': [ '-pthread' ],
             'ldflags': [ '-pthread' ],
           }],
-          [ 'visibility=="hidden" and gcc_version >= "4.0.0"', {
+          [ 'visibility=="hidden" and (clang==1 or gcc_version >= 40)', {
             'cflags': [ '-fvisibility=hidden' ],
           }],
         ],

gyp_uv

 #!/usr/bin/env python
+
 import glob
 import os
-import shlex
+import subprocess
 import sys
 
+CC = os.environ.get('CC', 'cc')
 script_dir = os.path.dirname(__file__)
 uv_root = os.path.normpath(script_dir)
+output_dir = os.path.join(os.path.abspath(uv_root), 'out')
 
 sys.path.insert(0, os.path.join(uv_root, 'build', 'gyp', 'pylib'))
 try:
@@ -14,9 +17,14 @@ except ImportError:
   print('You need to install gyp in build/gyp first. See the README.')
   sys.exit(42)
 
-# Directory within which we want all generated files (including Makefiles)
-# to be written.
-output_dir = os.path.join(os.path.abspath(uv_root), 'out')
+
+def compiler_version():
+  proc = subprocess.Popen(CC.split() + ['--version'], stdout=subprocess.PIPE)
+  is_clang = 'clang' in proc.communicate()[0].split('\n')[0]
+  proc = subprocess.Popen(CC.split() + ['-dumpversion'], stdout=subprocess.PIPE)
+  version = tuple(map(int, proc.communicate()[0].split('.')))
+  return (version, is_clang)
+
 
 def run_gyp(args):
   rc = gyp.main(args)
@@ -24,6 +32,7 @@ def run_gyp(args):
     print 'Error running GYP'
     sys.exit(rc)
 
+
 if __name__ == '__main__':
   args = sys.argv[1:]
 
@@ -49,12 +58,12 @@ if __name__ == '__main__':
 
   # There's a bug with windows which doesn't allow this feature.
   if sys.platform != 'win32':
-    # Tell gyp to write the Makefiles into output_dir
     args.extend(['--generator-output', output_dir])
-    # Tell make to write its output into the same dir
     args.extend(['-Goutput_dir=' + output_dir])
-    # Create Makefiles, not XCode projects
     args.extend('-f make'.split())
+    (major, minor), is_clang = compiler_version()
+    args.append('-Dgcc_version=%d' % (10 * major + minor))
+    args.append('-Dclang=%d' % int(is_clang))
 
   args.append('-Dtarget_arch=ia32')
   args.append('-Dcomponent=static_library')