[builtins] Drop -fnested-functions flag from tests

[arichardson]

Summary

This flag does nothing for clang and is apparently not supported by GCC:
aarch64-linux-gnu-gcc: error: unrecognized command-line option '-fnested-functions'; did you mean '-Wunused-function'?
It looks like it was maybe supported by Apple GCC, but that is no longer
a supported compiler.

compiler-rt/test/builtins/Unit/test

for FILE in $(ls *.c); do
     # prefer our implementation over the ones in libSystem.dylib
     EXTRA=
     if test $FILE = gcc_personality_test.c
     then
       # the gcc_personality_test.c requires a helper C++ program
       EXTRA="-fexceptions gcc_personality_test_helper.cxx -lstdc++ /usr/lib/libgcc_s.1.dylib"
       # the libgcc_s.1.dylib use at the end is a hack until libSystem contains _Unwind_Resume
     fi
-    if test $FILE = trampoline_setup_test.c
-    then
-      # this test requires an extra compiler option
-      EXTRA="-fnested-functions"
-    fi
     if test "$REMOTE" = "1"
     then 
       if gcc $CFLAGS $FILE ../../darwin_fat/Release/libcompiler_rt.a $LIBS $EXTRA -o ./remote/$FILE.exe
       then
         echo "Built $FILE.exe for $ARCH"
       else
         echo "$FILE failed to compile"
       fi

compiler-rt/test/builtins/Unit/trampoline_setup_test.c

-// RUN: %clang_builtins %s %librt -fnested-functions -o %t && %run %t
+// RUN: %clang_builtins %s %librt -o %t && %run %t
 // REQUIRES: librt_has_trampoline_setup
 
 #include <stdio.h>
 #include <string.h>
 #include <stdint.h>
 
 /*
  * Tests nested functions