Don't spend time initializing LLVM when running the driver (#14896)

Tiny start-up time optimization noticed while looking at how we do
PrettyStackTraceProgram. Also add PrettyStackTraceProgram to a few
more of our testing tools, via the new PROGRAM_START macro.

tools/swift-syntax-test/swift-syntax-test.cpp

@@ -21,6 +21,7 @@
 #include "swift/AST/DiagnosticEngine.h"
 #include "swift/AST/DiagnosticsFrontend.h"
 #include "swift/Basic/LangOptions.h"
+#include "swift/Basic/LLVMInitialize.h"
 #include "swift/Basic/SourceManager.h"
 #include "swift/Frontend/Frontend.h"
 #include "swift/Frontend/PrintingDiagnosticConsumer.h"
@@ -281,6 +282,7 @@ int dumpEOFSourceLoc(const char *MainExecutablePath,
 }// end of anonymous namespace
 
 int main(int argc, char *argv[]) {
+  PROGRAM_START(argc, argv);
   llvm::cl::ParseCommandLineOptions(argc, argv, "Swift Syntax Test\n");
 
   int ExitCode = EXIT_SUCCESS;