[llvm] Enable logf128 constant folding for hosts with 128bit long double (PR #104929)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-m68k-linux-cross` running on `suse-gary-m68k-cross` while building `llvm` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/27/builds/303

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

```
Step 5 (ninja check 1) failure: stage 1 checked (failure)
******************** TEST 'LLVM :: Transforms/InstSimplify/ConstProp/logf128.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/stage1/bin/opt < /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll -passes=instsimplify -S | /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/stage1/bin/FileCheck /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll
+ /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/stage1/bin/opt -passes=instsimplify -S
+ /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/stage1/bin/FileCheck /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll
/srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll:75:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: ret fp128 0xL00000000000000007FFF800000000000
              ^
<stdin>:41:35: note: scanning from here
define fp128 @log_e_negative_2() {
                                  ^
<stdin>:42:2: note: possible intended match here
 ret fp128 0xL0000000000000000FFFF800000000000
 ^
/srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll:107:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: ret fp128 0xL00000000000000007FFF800000000000
              ^
<stdin>:57:42: note: scanning from here
define fp128 @log_e_negative_infinity() {
                                         ^
<stdin>:58:2: note: possible intended match here
 ret fp128 0xL0000000000000000FFFF800000000000
 ^
/srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll:123:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: ret <2 x fp128> <fp128 0xL00000000000000007FFF800000000000, fp128 0xL00000000000000007FFF800000000000>
              ^
<stdin>:65:48: note: scanning from here
define <2 x fp128> @log_e_negative_2_vector() {
                                               ^
<stdin>:66:2: note: possible intended match here
 ret <2 x fp128> <fp128 0xL0000000000000000FFFF800000000000, fp128 0xL0000000000000000FFFF800000000000>
 ^

Input file: <stdin>
Check file: /srv/buildbot/workers/suse-gary-m68k-cross/clang-m68k-linux-cross/llvm/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll

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

Input was:
<<<<<<
            .
            .
            .
           36:  
           37: define fp128 @log_e_smallest_number_larger_than_one() { 
           38:  ret fp128 0xL00000000000000003F8F000000000000 
           39: } 
...

```

</details>

https://github.com/llvm/llvm-project/pull/104929