Re: Guiding principle for dropping LLVM versions?

Hi,

Can we also check if the clang's version is compatible with llvm's version in llvm.m4? I have multiple llvm toolchains installed on my system and I have to specify the $CLANG and $LLVM_CONFIG variables each time I build the server against a toolchain that is not present in $PATH. If one of the variables is missing, the build system will pick up a default one whose version might not be compatible with the other. E.g., If we use clang-16 and llvm-config-15, there will be issues when creating indexes for bitcodes at the end of installation.

There will be errors look like

```

LLVM ERROR: ThinLTO cannot create input file: Unknown attribute kind (86) (Producer: 'LLVM16.0.6' Reader: 'LLVM 15.0.7')
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0.      Program arguments: /usr/lib/llvm15/bin/llvm-lto -thinlto -thinlto-action=thinlink -o postgres.index.bc postgres/access/brin/brin.bc postgres/access/brin/brin_bloom.bc postgres/acces
s/brin/brin_inclusion.bc postgres/access/brin/brin_minmax.bc postgres/access/brin/brin_minmax_multi.bc postgres/access/brin/brin_pageops.bc postgres/access/brin/brin_revmap.bc postgres/acce
ss/brin/brin_tuple.bc postgres/access/brin/brin_validate.bc postgres/access/brin/brin_xlog.bc postgres/access/common/attmap.bc postgres/access/common/bufmask.bc postgres/access/common/detoa
st.bc postgres/access/common/heaptuple.bc postgres/access/common/indextuple.bc postgres/access/common/printsimple.bc postgres/access/common/printtup.bc postgres/access/common/relation.bc po
stgres/access/common/reloptions.bc postgres/access/common/scankey.bc postgres/access/common/session.bc postgres/access/common/syncscan.bc postgres/access/common/toast_compression.bc postgre
s/access/common/toast_internals.bc postgres/access/common/tupconvert.bc postgres/access/common/tupdesc.bc postgres/access/gin/ginarrayproc.bc postgres/access/gin/ginbtree.bc postgres/access
/gin/ginbulk.bc postgres/access/gin/gindatapage.bc postgres/access/gin/ginentrypage.bc postgres/access/gin/ginfast.bc postgres/access/gin/ginget.bc postgres/access/gin/gininsert.bc postgres
/access/gin/ginlogic.bc postgres/access/gin/ginpostinglist.bc postgres/access/gin/ginscan.bc postgres/access/gin/ginutil.bc postgres/access/gin/ginvacuum.bc postgres/access/gin/ginvalidate.
bc postgres/access/gin/ginxlog.bc postgres/access/gist/gist.bc postgres/access/gist/gistbuild.bc postgres/access/gist/gistbuildbuffers.bc postgres/access/gist/gistget.bc postgres/access/gis
t/gistproc.bc postgres/access/gist/gistscan.bc postgres/access/gist/gistsplit.bc postgres/access/gist/gistutil.bc postgres/access/gist/gistvacuum.bc postgres/access/gist/gistvalidate.bc pos
tgres/access/gist/gistxlog.bc postgres/access/hash/hash.bc postgres/access/hash/hash_xlog.bc postgres/access/hash/hashfunc.bc postgres/access/hash/hashinsert.bc postgres/access/hash/hashovf
l.bc postgres/access/hash/hashpage.bc postgres/access/hash/hashsearch.bc postgres/access/hash/hashsort.bc postgres/access/hash/hashutil.bc postgres/access/hash/hashvalidate.bc postgres/acce
ss/heap/heapam.bc postgres/access/heap/heapam_handler.bc postgres/access/heap/heapam_visibility.bc postgres/access/heap/heaptoast.bc postgres/access/heap/hio.bc postgres/access/heap/prunehe

```

If we can check the llvm-config versions and clang versions at the configuration phase we can detect the problem earlier.