Fix build-script to enable testing

Author: akkyie

build-script.py

@@ -167,7 +167,7 @@ def get_swiftpm_invocation(spm_exec, build_dir, parser_header_dir,
     if spm_exec == 'swift build':
         swiftpm_call = ['swift', 'build']
     elif spm_exec == 'swift test':
-        swiftpm_call = ['swift', 'test']
+        swiftpm_call = ['swift', 'test', '-Xswiftc', '-enable-testing']
     else:
         swiftpm_call = [spm_exec]