Make AST reading work better with LLVM_APPEND_VC_REV=NO

With LLVM_APPEND_VC_REV=NO, Modules/merge-lifetime-extended-temporary.cpp
would fail if it ran before a0f50d7316 (which changed
the serialization format) and then after, for these reasons:

1. With LLVM_APPEND_VC_REV=NO, the module hash before and after the
   change was the same.

2. Modules/merge-lifetime-extended-temporary.cpp is the only test
   we have that uses -fmodule-cache-path=%t that
   a) actually writes to the cache path
   b) doesn't do `rm -rf %t` at the top of the test

So the old run would write a module file, and then the new run would
try to load it, but the serialized format changed.

Do several things to fix this:

1. Include clang::serialization::VERSION_MAJOR/VERSION_MINOR in
   the module hash, so that when the AST format changes (...and
   we remember to bump these), we use a different module cache dir.
2. Bump VERSION_MAJOR, since a0f50d7316 changed the
   on-disk format in a way that a gch file written before that change
   can't be read after that change.
3. Add `rm -rf %t` to all tests that pass -fmodule-cache-path=%t.
   This is unnecessary from a correctness PoV after 1 and 2,
   but makes it so that we don't amass many cache dirs over time.
   (Arguably, it also makes it so that the test suite doesn't catch
   when we change the serialization format but don't bump
   clang::serialization::VERSION_MAJOR/VERSION_MINOR; oh well.)

Differential Revision: https://reviews.llvm.org/D73202

clang/include/clang/Serialization/ASTBitCodes.h

@@ -41,7 +41,7 @@ namespace serialization {
     /// Version 4 of AST files also requires that the version control branch and
     /// revision match exactly, since there is no backward compatibility of
     /// AST files at this time.
-    const unsigned VERSION_MAJOR = 8;
+    const unsigned VERSION_MAJOR = 9;
 
     /// AST file minor version number supported by this version of
     /// Clang.

clang/lib/Frontend/CompilerInvocation.cpp

@@ -41,6 +41,7 @@
 #include "clang/Lex/HeaderSearchOptions.h"
 #include "clang/Lex/PreprocessorOptions.h"
 #include "clang/Sema/CodeCompleteOptions.h"
+#include "clang/Serialization/ASTBitCodes.h"
 #include "clang/Serialization/ModuleFileExtension.h"
 #include "clang/StaticAnalyzer/Core/AnalyzerOptions.h"
 #include "llvm/ADT/APInt.h"
@@ -3635,6 +3636,11 @@ std::string CompilerInvocation::getModuleHash() const {
   // CityHash, but this will do for now.
   hash_code code = hash_value(getClangFullRepositoryVersion());
 
+  // Also include the serialization version, in case LLVM_APPEND_VC_REV is off
+  // and getClangFullRepositoryVersion() doesn't include git revision.
+  code = hash_combine(code, serialization::VERSION_MAJOR,
+                      serialization::VERSION_MINOR);
+
   // Extend the signature with the language options
 #define LANGOPT(Name, Bits, Default, Description) \
    code = hash_combine(code, LangOpts->Name);

clang/test/Modules/diagnostics.modulemap

@@ -1,3 +1,4 @@
+// RUN: rm -rf %t
 // RUN: not %clang_cc1 -fmodules -fmodules-cache-path=%t -fmodule-map-file=%S/Inputs/diagnostics-aux.modulemap -fmodule-map-file=%s -fsyntax-only -x c++ /dev/null 2>&1 | FileCheck %s --implicit-check-not error:
 
 // CHECK: In file included from {{.*}}diagnostics-aux.modulemap:3:

clang/test/Modules/exception-spec.cpp

@@ -1,3 +1,4 @@
+// RUN: rm -rf %t
 // RUN: %clang_cc1 -x c++ -std=c++17 -fmodules -fmodules-local-submodule-visibility -fmodules-cache-path=%t %s -verify
 
 // expected-no-diagnostics

clang/test/Modules/merge-lifetime-extended-temporary.cpp

@@ -1,3 +1,4 @@
+// RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-lifetime-extended-temporary -verify -std=c++11 %s -DORDER=1
 // RUN: %clang_cc1 -fmodules -fimplicit-module-maps -fmodules-cache-path=%t -x c++ -I%S/Inputs/merge-lifetime-extended-temporary -verify -std=c++11 %s -DORDER=2
 

clang/test/Modules/objc-method-redecl.m

@@ -1,3 +1,4 @@
+// RUN: rm -rf %t
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -x objective-c-header -emit-pch %S/Inputs/objc-method-redecl.h -o %t.pch -Wno-objc-root-class
 // RUN: %clang_cc1 -fmodules -fmodules-cache-path=%t -x objective-c -include-pch %t.pch %s -verify -Wno-objc-root-class
 // expected-no-diagnostics

clang/test/Modules/using-decl-inheritance.cpp

@@ -1,3 +1,4 @@
+// RUN: rm -rf %t
 // RUN: %clang_cc1 -x c++ -fmodules -fmodules-local-submodule-visibility -fmodules-cache-path=%t %s -verify
 // RUN: %clang_cc1 -x c++ -fmodules -fmodules-cache-path=%t %s -verify