Don't use CLANG_VERSION_MAJOR to check that the value passed to -fclang-abi-compat= is valid (llvm#123998)

Use LLVM_VERSION_MAJOR instead as the maximum allowed value. This change
is needed to fix regression tests that fail when vendors set
CLANG_VERSION_MAJOR to a value that is lower than LLVM_VERSION_MAJOR
when building the compiler.

For example, clang/test/CodeGenCXX/mangle-concept.cpp fails with the
following error if -DCLANG_VERSION_MAJOR=17 is passed to cmake:

invalid value '19' in '-fclang-abi-compat=19'

Author: ahatanak

clang/CMakeLists.txt

@@ -331,6 +331,7 @@ if(NOT DEFINED CLANG_VERSION_SUFFIX)
   set(CLANG_VERSION_SUFFIX ${LLVM_VERSION_SUFFIX})
 endif()
 set(CLANG_VERSION "${CLANG_VERSION_MAJOR}.${CLANG_VERSION_MINOR}.${CLANG_VERSION_PATCHLEVEL}${CLANG_VERSION_SUFFIX}")
+set(MAX_CLANG_ABI_COMPAT_VERSION "${LLVM_VERSION_MAJOR}")
 message(STATUS "Clang version: ${CLANG_VERSION}")
 
 # Configure the Version.inc file.

clang/include/clang/Basic/Version.inc.in

@@ -4,3 +4,4 @@
 #define CLANG_VERSION_MAJOR_STRING "@CLANG_VERSION_MAJOR@"
 #define CLANG_VERSION_MINOR @CLANG_VERSION_MINOR@
 #define CLANG_VERSION_PATCHLEVEL @CLANG_VERSION_PATCHLEVEL@
+#define MAX_CLANG_ABI_COMPAT_VERSION @MAX_CLANG_ABI_COMPAT_VERSION@

clang/lib/Frontend/CompilerInvocation.cpp

@@ -4413,7 +4413,7 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     // y or y.0 (4 <= y <= current version).
     if (!VerParts.first.starts_with("0") &&
         !VerParts.first.getAsInteger(10, Major) && 3 <= Major &&
-        Major <= CLANG_VERSION_MAJOR &&
+        Major <= MAX_CLANG_ABI_COMPAT_VERSION &&
         (Major == 3
              ? VerParts.second.size() == 1 &&
                    !VerParts.second.getAsInteger(10, Minor)