Build C API tests with clang

Fedora 44 appears to have shipped a version of GCC 16 containing PR120322
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120322), which causes
narrow integer arguments not to be zero-extended when they are passed to
functions. The bug caused spurious failures in the `callind` test case
by passing `SPIDIR_TYPE_NONE` as 0xffffffff and triggering UB in the rust
code.

Just switch to clang for now (and probably forever?).

Author: nmraz

c-api-tests/run.sh

@@ -4,6 +4,8 @@ set -euo pipefail
 
 cd $(dirname $(readlink -f "$0"))
 
+export CC=clang
+export CXX=clang++
 export CMAKE_EXPORT_COMPILE_COMMANDS=ON
 export CTEST_OUTPUT_ON_FAILURE=1