[llvm] Enable aggressive constant merge in GlobalMerge for AIX (PR #113956)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-x86_64-debian-fast` running on `gribozavr4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/56/builds/11123

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/PowerPC/gcov_ctr_ref_init.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 3: /b/1/clang-x86_64-debian-fast/llvm.obj/bin/llc < /b/1/clang-x86_64-debian-fast/llvm.src/llvm/test/CodeGen/PowerPC/gcov_ctr_ref_init.ll | /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck --check-prefixes=CHECK,CHECK-RW /b/1/clang-x86_64-debian-fast/llvm.src/llvm/test/CodeGen/PowerPC/gcov_ctr_ref_init.ll
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/FileCheck --check-prefixes=CHECK,CHECK-RW /b/1/clang-x86_64-debian-fast/llvm.src/llvm/test/CodeGen/PowerPC/gcov_ctr_ref_init.ll
+ /b/1/clang-x86_64-debian-fast/llvm.obj/bin/llc
/b/1/clang-x86_64-debian-fast/llvm.src/llvm/test/CodeGen/PowerPC/gcov_ctr_ref_init.ll:23:15: error: CHECK-NEXT: is not on the line after the previous match
; CHECK-NEXT: .extern .llvm_gcda_start_file[PR]
              ^
<stdin>:261:2: note: 'next' match was here
 .extern .llvm_gcda_start_file[PR]
 ^
<stdin>:232:19: note: previous match ended here
__llvm_gcov_ctr.1:
                  ^
<stdin>:233:1: note: non-matching line after previous match is here
 .csect L.._MergedGlobals.1[RW],4
^

Input file: <stdin>
Check file: /b/1/clang-x86_64-debian-fast/llvm.src/llvm/test/CodeGen/PowerPC/gcov_ctr_ref_init.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
         .
         .
         .
       256:  .vbyte 4, 875575338 # 0x3430382a 
       257:  .vbyte 4, 3493522647 # 0xd03aecd7 
       258:  .vbyte 4, 2 # 0x2 
       259:  .vbyte 4, L.._MergedGlobals.1[RW]+32 
       260:  .vbyte 4, L.._MergedGlobals.1[RW]+16 
       261:  .extern .llvm_gcda_start_file[PR] 
next:23      !~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~  error: match on wrong line
       262:  .extern .llvm_gcda_emit_function[PR] 
       263:  .extern .llvm_gcda_emit_arcs[PR] 
       264:  .extern .llvm_gcda_summary_info[PR] 
       265:  .extern .llvm_gcda_end_file[PR] 
       266:  .csect __llvm_gcov_ctr_section[RW],3 
         .
         .
         .
>>>>>>

--

...

```

</details>

https://github.com/llvm/llvm-project/pull/113956