build: add default build flags to gyp script

http_parser.gyp

@@ -12,6 +12,7 @@
       #       RuntimeLibrary MUST MATCH across the entire project
       'Debug': {
         'defines': [ 'DEBUG', '_DEBUG' ],
+        'cflags': [ '-Wall', '-Wextra', '-O0', '-g', '-ftrapv' ],
         'msvs_settings': {
           'VCCLCompilerTool': {
             'RuntimeLibrary': 1, # static debug
@@ -20,6 +21,7 @@
       },
       'Release': {
         'defines': [ 'NDEBUG' ],
+        'cflags': [ '-Wall', '-Wextra', '-O3' ],
         'msvs_settings': {
           'VCCLCompilerTool': {
             'RuntimeLibrary': 0, # static release