[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-with-thin-lto-ubuntu` running on `as-worker-92` while building `llvm` at step 7 "test-stage1-compiler".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/127/builds/617

Here is the relevant piece of the build log for the reference:
```
Step 7 (test-stage1-compiler) failure: build (failure)
...
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using ld64.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld64.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using wasm-ld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/wasm-ld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/utils/lit/tests/lit.cfg:111: warning: Setting a timeout per test not supported. Requires the Python psutil module but it could not be found. Try installing it via pip or via your operating system's package manager.
 Some tests will be skipped and the --timeout command line argument will not work.
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using ld.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using lld-link: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/lld-link
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using ld64.lld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/ld64.lld
llvm-lit: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/utils/lit/lit/llvm/config.py:508: note: using wasm-ld: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/wasm-ld
-- Testing: 80096 tests, 72 workers --
Testing:  0.. 10.. 20.. 30.. 40.. 50.. 60.. 70.. 
FAIL: LLVM :: Transforms/InstSimplify/ConstProp/logf128.ll (64327 of 80096)
******************** TEST 'LLVM :: Transforms/InstSimplify/ConstProp/logf128.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
RUN: at line 2: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/opt < /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll -passes=instsimplify -S | /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/FileCheck /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll
+ /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/opt -passes=instsimplify -S
+ /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/build/stage1/bin/FileCheck /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll
/home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/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
 ^
/home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/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
 ^
/home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/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: /home/buildbot/as-worker-92/clang-with-thin-lto-ubuntu/llvm-project/llvm/test/Transforms/InstSimplify/ConstProp/logf128.ll

```

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