[PGO] Add tests for modules with only globals and function declarations (#93764)

When a module contains globals and/or function declarations only, the
'__llvm_profile_raw_version' variable should not be generated because
the module was not instrumented at all.

NFC

Author: samolisov

llvm/test/Transforms/PGOProfile/available_externally_functions.ll

@@ -0,0 +1,17 @@
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN --check-prefix=GEN-COMDAT
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
+; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
+; GEN: @__profn_foo = linkonce_odr hidden constant [3 x i8] c"foo"
+; GEN: @__profn_bar = linkonce_odr hidden constant [3 x i8] c"bar"
+
+define available_externally hidden void @foo() {
+  ret void
+}
+
+define available_externally i32 @bar() {
+  ret i32 42
+}

llvm/test/Transforms/PGOProfile/declarations_only.ll

@@ -0,0 +1,13 @@
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN --check-prefix=GEN-COMDAT
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
+; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
+; GEN-NOT: @__profn_test_1 = private constant [6 x i8] c"test_1"
+; GEN-NOT: @__profn_test_2 = private constant [6 x i8] c"test_2"
+
+declare i32 @test_1(i32 %i)
+
+declare i32 @test_2(i32 %i)

llvm/test/Transforms/PGOProfile/global_variables_only.ll

@@ -0,0 +1,9 @@
+; RUN: opt < %s -passes=pgo-instr-gen -S | FileCheck %s --check-prefix=GEN-COMDAT
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+; GEN-COMDAT: $__llvm_profile_raw_version = comdat any
+; GEN-COMDAT: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
+
+@var = internal unnamed_addr global [35 x ptr] zeroinitializer, align 16