Fix make on srcdir != builddir

[fd00]

The make check command fails because the include path is not appropriate for the Makefile generated by autotools when the source and build directories are different.

$ cd /tmp
$ git clone https://github.com/recp/cglm.git
$ cd cglm
$ autoreconf -fiv
$ mkdir build
$ cd build
$ ../configure
:
$ make check
:
/Library/Developer/CommandLineTools/usr/bin/make  test/tests
  CC       test/tests-runner.o
In file included from ../test/runner.c:8:
../test/include/common.h:31:10: fatal error: 'cglm/cglm.h' file not found
   31 | #include <cglm/cglm.h>
      |          ^~~~~~~~~~~~~
1 error generated.
make[1]: *** [test/tests-runner.o] Error 1
make: *** [check-am] Error 2

[Copilot]

Pull Request Overview

This PR fixes the make check failure when the source directory differs from the build directory by updating the include path in the test build flags.

• Changed relative include flag from -I./include to -I$(srcdir)/include
• Ensures headers are found when srcdir != builddir

[Copilot]

[nitpick] Preprocessor include paths are conventionally set in CPPFLAGS rather than CFLAGS; consider moving the -I$(srcdir)/include flag to check_CPPFLAGS or AM_CPPFLAGS for clearer separation of concerns.

[fd00]

Sorry I forgot to disable Automatic Copilot code review.

[recp]

@fd00 the PR is merged, thanks for your contributions 🚀