MIPS: Pass -fp32 flag to the compiler when building for loongson

BUG=

Review URL: https://codereview.chromium.org/1384453003

Cr-Commit-Position: refs/heads/master@{#31065}

build/toolchain.gypi

@@ -638,8 +638,8 @@
                       '_MIPS_ARCH_LOONGSON',
                       'FPU_MODE_FP32',
                     ],
-                    'cflags!': ['-mfp64', '-mfp32', '-mfpxx'],
-                    'cflags': ['-mips3', '-Wa,-mips3'],
+                    'cflags!': ['-mfp64', '-mfpxx'],
+                    'cflags': ['-mips3', '-Wa,-mips3', '-mfp32'],
                   }],
                 ],
               }, {