Compile JSC on Windows and Linux as well

Ref. v8/web-tooling-benchmark#29 (comment)

Author: mathiasbynens

src/build.py

@@ -948,7 +948,7 @@ def Jsc():
     command = ['xcrun', PREBUILT_CMAKE_BIN, '-Wno-dev',
                '..', '-G', 'Ninja',
                '-DCMAKE_BUILD_TYPE="Release"',
-               '-DPORT=Mac',
+               '-DPORT=JSCOnly',
                '-DENABLE_WEBASSEMBLY=ON']
 
     command.extend(OverrideCMakeCompiler())