X87: use more suitable build flag

BUG=
R=danno@chromium.org

Review URL: https://codereview.chromium.org/305643005

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21603 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/toolchain.gypi

@@ -292,8 +292,7 @@
         'defines': [
           'V8_TARGET_ARCH_X87',
         ],
-        'cflags': ['-mfpmath=387'],
-        'ldflags': ['-mfpmath=387'],
+        'cflags': ['-march=i586'],
       }],  # v8_target_arch=="x87"
       ['v8_target_arch=="mips"', {
         'defines': [