Fix shared library build errors.

R=jkummerow@chromium.org
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10389203

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11591 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

SConstruct

@@ -101,14 +101,14 @@ LIBRARY_FLAGS = {
     'os:linux': {
       'CCFLAGS':      ['-ansi'] + GCC_EXTRA_CCFLAGS,
       'library:shared': {
-        'CPPDEFINES': ['V8_SHARED'],
+        'CPPDEFINES': ['V8_SHARED', 'BUILDING_V8_SHARED'],
         'LIBS': ['pthread']
       }
     },
     'os:macos': {
       'CCFLAGS':      ['-ansi', '-mmacosx-version-min=10.4'],
       'library:shared': {
-        'CPPDEFINES': ['V8_SHARED']
+        'CPPDEFINES': ['V8_SHARED', 'BUILDING_V8_SHARED'],
       }
     },
     'os:freebsd': {