mips: Really build the MIPS V8 code

2008d2d40e was not rebased properly and
should have used the V8_TARGET_ARCH to add the MIPS code to the build.

Change-Id: Idf0c183fca63da0fa9f9aa8d091a764b88c888f5
Reviewed-by: Aaron Kennedy <aaron.kennedy@nokia.com>

src/v8/v8.pri

@@ -210,9 +210,7 @@ SOURCES += \
     $$V8SRC/x64/macro-assembler-x64.cc \
     $$V8SRC/x64/regexp-macro-assembler-x64.cc \
     $$V8SRC/x64/stub-cache-x64.cc
-}
-
-arch_mips {
+} else:equals(V8_TARGET_ARCH, mips) {
 DEFINES += V8_TARGET_MIPS
 SOURCES += \
     $$V8SRC/mips/assembler-mips.cc \