Set version based on port version, remove usage of -O3

Index: build/gen.py
--- build/gen.py.orig
+++ build/gen.py
@@ -216,25 +216,16 @@ def main(argv):
 
 
 def GenerateLastCommitPosition(host, header):
-  ROOT_TAG = 'initial-commit'
-  describe_output = subprocess.check_output(
-      ['git', 'describe', 'HEAD', '--abbrev=12', '--match', ROOT_TAG],
-      shell=host.is_windows(), cwd=REPO_ROOT)
-  mo = re.match(ROOT_TAG + '-(\d+)-g([0-9a-f]+)', describe_output.decode())
-  if not mo:
-    raise ValueError(
-        'Unexpected output from git describe when generating version header')
-
   contents = '''// Generated by build/gen.py.
 
 #ifndef OUT_LAST_COMMIT_POSITION_H_
 #define OUT_LAST_COMMIT_POSITION_H_
 
 #define LAST_COMMIT_POSITION_NUM %s
-#define LAST_COMMIT_POSITION "%s (%s)"
+#define LAST_COMMIT_POSITION "%s"
 
 #endif  // OUT_LAST_COMMIT_POSITION_H_
-''' % (mo.group(1), mo.group(1), mo.group(2))
+''' % (os.environ['GN_VERSION'],os.environ['GN_VERSION'])
 
   # Only write/touch this file if the commit position has changed.
   old_contents = ''
@@ -395,10 +386,8 @@ def WriteGNNinja(path, platform, host, options, args_l
       cflags.extend(['-O0', '-g'])
     else:
       cflags.append('-DNDEBUG')
-      cflags.append('-O3')
       if options.no_strip:
         cflags.append('-g')
-      ldflags.append('-O3')
       # Use -fdata-sections and -ffunction-sections to place each function
       # or data item into its own section so --gc-sections can eliminate any
       # unused functions and data items.