mpc: Unset LIBS before configuring

[guy-david]

mpc/1.3.1

On systems that do not have libmpfr.so.6 installed, I fail to configure this package:

configure:3919: checking whether we are cross compiling
configure:3927: clang-16 -o conftest  -m64 -O3 -I/local/users/guyd/conan/.conan/data/gmp/6.3.0/_/_/package/581209b46b4309cd0f7261e5f10bfe21d5d4fc08/include -I/local/users/guyd/conan/.conan/data/mpfr/4.2.0/_/_/package/e4297c5e065990fd51a06a706f890cb821c50fae/include  -DNDEBUG -I/local/users/guyd/conan/.conan/data/mpfr/4.2.0/_/_/package/e4297c5e065990fd51a06a706f890cb821c50fae/include -I/local/users/guyd/conan/.conan/data/gmp/6.3.0/_/_/package/581209b46b4309cd0f7261e5f10bfe21d5d4fc08/include -L/local/users/guyd/conan/.conan/data/gmp/6.3.0/_/_/package/581209b46b4309cd0f7261e5f10bfe21d5d4fc08/lib -L/local/users/guyd/conan/.conan/data/mpfr/4.2.0/_/_/package/e4297c5e065990fd51a06a706f890cb821c50fae/lib  -m64 -L/local/users/guyd/conan/.conan/data/mpfr/4.2.0/_/_/package/e4297c5e065990fd51a06a706f890cb821c50fae/lib -L/local/users/guyd/conan/.conan/data/gmp/6.3.0/_/_/package/581209b46b4309cd0f7261e5f10bfe21d5d4fc08/lib conftest.c -lm -lmpfr -lgmpxx -lgmp -lm >&5
configure:3931: $? = 0
configure:3938: ./conftest
./conftest: error while loading shared libraries: libmpfr.so.6: cannot open shared object file: No such file or directory

My theory is that the AutoToolsToolchain populates the LIBS environment variable with the package's dependencies (i.e. -lgmp, -lmpfr), MPC then adds these to the implicit list of libraries it should link (LIBS libraries to pass to the linker, e.g. -l<library>). That works fine during linking but to actually run the resulting executable, one needs to set LD_LIBRARY_PATH or compile with an RPATH which I believe is undesirable.
I think that it's not MPC at fault in this case because it manually configures the paths to its dependencies, so therefore I limited the scope of this "fix" but I'd rather someone with more experience will take a look.

---

• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[CLAassistant]

All committers have signed the CLA.

[conan-center-bot]

Conan v1 pipeline ❌

Sorry, the build is only launched for Access Request users. You can request access writing in this issue.

Conan v2 pipeline ❌

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

The v2 pipeline failed. Please, review the errors and note this is required for pull requests to be merged. In case this recipe is still not ported to Conan 2.x, please, ping @conan-io/barbarians on the PR and we will help you.

See details:

Sorry, the build is only launched for Access Request users. You can request access writing in this issue.

[jcar87]

Hi @guy-david, thank you for your contribution.

I believe something else might be happening that explains what you are experiencing - libmpfr is listed as a conan dependency, and I can see logic in the recipe to handle this appropriately.

Could you please provide details of your conan profile and which conan command you are invoking that results in this error so that we could troubleshoot this on our end? thanks!