pam: Get preloaded libraries paths using compiler

In order to run pam module tests we need to pass the libraries via
LD_PRELOAD, this supports a list of library paths, so use the compiler in
order to find their full paths (with soname) and check their presence.

In order to support linker scripts we need to introduce a workaround.
See meson issue https://github.com/mesonbuild/meson/issues/6880

tests/pam/meson.build

@@ -4,6 +4,31 @@ tests = [
     'test_pam_fprintd',
 ]
 
+preloaded_libs = [
+    'pam_wrapper'
+]
+pam_tests_ld_preload = []
+
+foreach libname: preloaded_libs
+    lib = run_command(meson.get_compiler('c'),
+        '-print-file-name=lib@0@.so'.format(libname)
+    ).stdout().strip()
+
+    # Support linker script files
+    if run_command('grep', '-qI', '^INPUT', files(lib)).returncode() == 0
+        out = run_command('cat', lib).stdout()
+        lib = out.split('(')[1].split(')')[0].strip()
+    endif
+
+    if lib != '' and lib[0] == '/'
+        message('Found library @0@ as @1@'.format(libname, lib))
+        pam_tests_ld_preload += '@0@'.format(files(lib)[0])
+    else
+        tests = []
+        warning('No library found for ' + libname + ', skipping PAM tests')
+    endif
+endforeach
+
 foreach t: tests
     python_tests += [
         {
@@ -12,7 +37,7 @@ foreach t: tests
             'env': [
                 'TOPBUILDDIR=' + meson.build_root(),
                 'TOPSRCDIR=' + meson.source_root(),
-                'LD_PRELOAD=libpam_wrapper.so',
+                'LD_PRELOAD=' + ' '.join(pam_tests_ld_preload),
                 'PAM_WRAPPER=1',
                 'PAM_WRAPPER_DEBUGLEVEL=2',
                 'PAM_WRAPPER_SERVICE_DIR=' + meson.current_build_dir() / 'services',