Set the default compiler for X87 to GCC.

Compiling v8 for X87 platform with clang compiler leads to some test case failure.
So we set the default compiler for X87 to GCC.

BUG=

Review URL: https://codereview.chromium.org/1031793002

Cr-Commit-Position: refs/heads/master@{#27706}

build/standalone.gypi

@@ -146,7 +146,8 @@
       }, {
         'v8_enable_gdbjit%': 0,
       }],
-      ['(OS=="linux" or OS=="mac") and (target_arch=="ia32" or target_arch=="x64")', {
+      ['(OS=="linux" or OS=="mac") and (target_arch=="ia32" or target_arch=="x64") and \
+        (v8_target_arch!="x87")', {
         'clang%': 1,
       }, {
         'clang%': 0,