Make flang driver stuff work on macOS

6bf55804 added special-case code for TY_PP_Fortran to
ToolChain::LookupTypeForExtension(), but
Darwin::LookupTypeForExtension() overrode that method without calling
the superclass implementation.

Make it call the superclass implementation to fix things.

Differential Revision: https://reviews.llvm.org/D69636

clang/lib/Driver/ToolChains/Darwin.cpp

@@ -737,7 +737,7 @@ Darwin::Darwin(const Driver &D, const llvm::Triple &Triple, const ArgList &Args)
       CudaInstallation(D, Triple, Args) {}
 
 types::ID MachO::LookupTypeForExtension(StringRef Ext) const {
-  types::ID Ty = types::lookupTypeForExtension(Ext);
+  types::ID Ty = ToolChain::lookupTypeForExtension(Ext);
 
   // Darwin always preprocesses assembly files (unless -x is used explicitly).
   if (Ty == types::TY_PP_Asm)

clang/test/Driver/flang/flang.f90

@@ -1,7 +1,3 @@
-! D63607 made mac builders unhappy by failing this test, and it isn't
-! yet obvious why. Mark as unsupported as a temporary measure.
-! UNSUPPORTED: darwin
-
 ! Check that flang -fc1 is invoked when in --driver-mode=flang.
 
 ! This is a copy of flang_ucase.F90 because the driver has logic in it which