Include setjmp.h unconditionally in asan_test_utils.h

It's used in asan_test.cc also on Windows, and my build was failing
with:

C:/src/llvm/projects/compiler-rt/lib/asan/tests/asan_test.cc:549:28: error: unknown type name 'jmp_buf'
NOINLINE void LongJmpFunc1(jmp_buf buf) {
                           ^
C:/src/llvm/projects/compiler-rt/lib/asan/tests/asan_test.cc:569:10: error: unknown type name 'jmp_buf'
  static jmp_buf buf;
         ^

I couldn't find what changed to make this not work anymore, but this should fix
it.

llvm-svn: 303273