Add AST_SIGNATURE record to unhashed control block of pcm files (Patch series 2/3)

[dang]

Summary

This lets users of PCM get a clean hash of the AST for uniquing based
on that. This required looking up implicit modules in the module offset map to
be looked up by name instead of by file path.

The previous patch is at D79993.
The next patch is at D80003.

[dang]

Should I add the test here or in the clang-scan-deps patch?

[Bigcheese]

In D79998#2038430, @dang wrote:

Should I add the test here or in the clang-scan-deps patch?

It's best to have a test in every non-nfc patch. You should be able to test this with llvm-bcanalyzer.

[dang]

Add a small bug fix and test case

[dang]

Uploaded the wrong diff

[dang]

This revision is superseded by D80383

clang/test/Modules/ASTSignature.c

+// RUN: rm -rf %t
+// RUN: %clang_cc1 -iquote %S/Inputs/ASTHash/ -fsyntax-only -fmodules \
+// RUN:   -fimplicit-module-maps -fmodules-strict-context-hash \
+// RUN:   -fmodules-cache-path=%t %s -Rmodule-build 2> %t1
+// RUN: %clang_cc1 -iquote "/dev/null" -iquote %S/Inputs/ASTHash/ -fsyntax-only \
+// RUN:   -fmodules -fimplicit-module-maps -fmodules-strict-context-hash \
+// RUN:   -fmodules-cache-path=%t %s -Rmodule-build 2> %t2
+// RUN: cat %t1 | grep "remark: building module 'MyHeader2'" | cut -d "'" -f 4 \
+// RUN:  | while read -r MODULE; do llvm-bcanalyzer --dump --disable-histogram \
+// RUN:  $MODULE | grep "AST_SIGNATURE" > %t1.sig; done
+// RUN: cat %t2 | grep "remark: building module 'MyHeader2'" | cut -d "'" -f 4 \
+// RUN:  | while read -r MODULE; do llvm-bcanalyzer --dump --disable-histogram \
+// RUN:  $MODULE | grep "AST_SIGNATURE" > %t1.sig; done
+// RUN: diff %t1.sig %t2.sig
+
+#include "my_header_2.h"
+
+my_int var = 42;

clang/test/Modules/Inputs/ASTHash/module.modulemap

+module MyHeader1 {
+  header "my_header_1.h"
+}
+
+module MyHeader2 {
+  header "my_header_2.h"
+  export *
+}

clang/test/Modules/Inputs/ASTHash/my_header_1.h

+typedef int my_int;

clang/test/Modules/Inputs/ASTHash/my_header_2.h

+#include "my_header_1.h"
+
+extern my_int var;