[RawProfReader]When constructing symbol table, read the MD5 of function name...

[RawProfReader]When constructing symbol table, read the MD5 of function name in the proper byte order (#76312)

Before this patch, when the field `NameRef` is generated in little-endian systems and read back in big-endian systems, the information gets dropped.
- The bug gets caught by a buildbot
https://lab.llvm.org/buildbot/#/builders/94/builds/17931. In the error message (pasted below),
two indirect call targets are not imported.

```
   ; IMPORTS-DAG: Import _Z7callee1v
               ^
<stdin>:1:1: note: scanning from here
main.ll: Import _Z11global_funcv from lib.cc
^
<stdin>:1:10: note: possible intended match here
main.ll: Import _Z11global_funcv from lib.cc
         ^
Input file: <stdin>
Check file:
/home/uweigand/sandbox/buildbot/clang-s390x-linux/llvm/llvm/test/Transforms/PGOProfile/thinlto_indirect_call_promotion.ll
-dump-input=help explains the following input dump.
Input was:
<<<<<<
          1: main.ll: Import _Z11global_funcv from lib.cc 
dag:34'0 X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match
found
dag:34'1 ? possible intended match
```

[This commit](https://github.com/llvm/llvm-project/commit/b3999246b1a93bd8e6dc7acac36a7d57fac96542#diff-b196b796c5a396c7cdf93b347fe47e2b29b72d0b7dd0e2b88abb964d376ee50e) gates the fix by flag and provide test data by creating big-endian profiles (rather than reading the little-endian data on a big-endian system that might require a VM).

- [This](https://github.com/llvm/llvm-project/commit/b3999246b1a93bd8e6dc7acac36a7d57fac96542#diff-643176077ddbe537bd0a05d2a8a53bdff6339420a30e8511710bf232afdda8b9) is a hexdump of little-endian profile data, and [this](https://github.com/llvm/llvm-project/commit/b3999246b1a93bd8e6dc7acac36a7d57fac96542#diff-1736a3ee25dde02bba55d670df78988fdb227e5a85b94b8707cf182cf70b28f0) is the big-endian version of it.
- The [README.md](https://github.com/llvm/llvm-project/commit/b3999246b1a93bd8e6dc7acac36a7d57fac96542#diff-6717b6a385de3ae60ab3aec9638af2a43b55adaf6784b6f0393ebe1a6639438b) shows the result of `llvm-profdata show -ic-targets` before and after the fix when the profile is in big-endian.