[clang] Produce a "multiversion" annotation in textual AST output.

This change adds a "multiversion" annotation to textual AST output.
For example:
  FunctionDecl 0xb6628b0 <t.c:1:1, col:13> col:5 multiversion foo 'int (void)'

Reviewed By: aaron.ballman

Differential Revision: https://reviews.llvm.org/D121961

clang/lib/AST/TextNodeDumper.cpp

@@ -283,6 +283,8 @@ void TextNodeDumper::Visit(const Decl *D) {
       OS << " constexpr";
     if (FD->isConsteval())
       OS << " consteval";
+    if (FD->isMultiVersion())
+      OS << " multiversion";
   }
 
   if (!isa<FunctionDecl>(*D)) {

clang/test/AST/ast-dump-funcs-multiversion.c

@@ -0,0 +1,23 @@
+// Test without serialization:
+// RUN: %clang_cc1 -triple x86_64-pc-linux -ast-dump -ast-dump-filter Test %s \
+// RUN: | FileCheck --strict-whitespace %s
+//
+// Test with serialization:
+// RUN: %clang_cc1 -triple x86_64-pc-linux -emit-pch -o %t %s
+// RUN: %clang_cc1 -x c -triple x86_64-pc-linux -include-pch %t \
+// RUN:            -ast-dump-all -ast-dump-filter Test /dev/null \
+// RUN: | sed -e "s/ <undeserialized declarations>//" -e "s/ imported//" \
+// RUN: | FileCheck --strict-whitespace %s
+
+void TestUnattributedMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestUnattributedMVF
+__attribute__((target("default"))) void TestUnattributedMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} prev 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestUnattributedMVF
+
+__attribute__((target("mmx"))) void TestNonMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} TestNonMVF
+
+__attribute__((target("mmx"))) void TestRetroMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestRetroMVF
+__attribute__((target("sse"))) void TestRetroMVF(void);
+// CHECK:      FunctionDecl 0x{{[^ ]*}} <{{.*}}> col:{{[0-9]*}} multiversion TestRetroMVF