cmake should make use of pkgconfig to detect shared libuv and gmp libs correctly

[juhp]

Prerequisites

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Description

With lean4 built from source on Linux /usr/lib/libuv.so and /usr/lib/libgmp.so are being passing directly to be linked by gcc (rather than -luv and -lgmp etc).

This causes many warnings from gcc: see below.

I am not good with cmake and so far failed to come up with a viable patch for this:
the current cmake (as of 4.13/4.14) in src/cmake/Modules/ leads to GMP_LIBRARIES=/usr/lib/libgmp.so
and LIBUV_LIBRARIES=/usr/lib/libuv.so on Linux which is not desired (at least for gcc).
I suppose I could also try clang - is that recommended for Linux builds?
I tried to use the cmake PkgConfig module macros but failed to get the right kind of output (boggle).

Note pkgconf is a compatible replacement of pkg-config: they are mostly equivalent.
It doesn't matter whether pkgconf or pkg-config is used.

For reference on Fedora Linux:

$ pkgconf --libs libuv
-luv -lpthread -ldl -lrt

Whether all those are strictly needed I dunno, but they are listed.
But this is what LIBUV_LIBRARIES should equal or at the very least -luv.

Context

[Broader context that the issue occurred in. If there was any prior discussion on the Lean Zulip, link it here as well.]

Steps to Reproduce

Expected behavior:

No unused linker warnings

Actual behavior:

$ lake build
:
ℹ [9/27] Replayed Curl.Errors:c.o
info: stderr:
gcc: warning: /usr/lib64/libuv.so: linker input file unused because linking not done
ℹ [10/27] Replayed Curl.CurlM:c.o
info: stderr:
gcc: warning: /usr/lib64/libuv.so: linker input file unused because linking not done
ℹ [11/27] Replayed Curl.HeaderData:c.o
info: stderr:
gcc: warning: /usr/lib64/libuv.so: linker input file unused because linking not done
ℹ [17/27] Replayed Main:c.o
info: stderr:
gcc: warning: /usr/lib64/libuv.so: linker input file unused because linking not done
:

(This is with patched in -lgmp, so normally there would be double the number of warnings.)

Versions

$ lean --version
Lean (version 4.13.0, Release)

on Fedora Linux

Additional Information

I am currently working around it by directly patching pkgconf --libs output into src/cmake/Modules/Find*.cmake (and for stage0 of course).

See fedora-haskell/lean4@c88870c

Impact

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[Kha]

@tydeu Should be fixed with #6176 not passing LEAN_EXTRA_LINKER_FLAGS to codegen anymore?