MDEV-24577: Fix warnings generated during compilation of...

MDEV-24577: Fix warnings generated during compilation of plugin/auth_pam/testing/pam_mariadb_mtr.c on FreeBSD

Compiler warnings generated on building MariaDB server for BSD has the same
reason as in case building is performed on MacOS. Both platforms do use
clang as a C/C++ compiler. So, fix the compiler warnings in case the compiler
is clang doesn't matter what kind of building platform do we use for building.

This is a follow-up patch for the following bug reports:
  MDEV-23564: CMAKE failing due to deprecated Apple GSS method
  MDEV-23935: Fix warnings generated during compilation of
              plugin/auth_pam/testing/pam_mariadb_mtr.c on MacOS

libmariadb @ 01866332

-Subproject commit e38244220646a7e95c9be22576460aa7a4eb715f
+Subproject commit 018663324bf9cbe11b0b2191c6fb6c10564bb4e5

plugin/auth_gssapi/CMakeLists.txt

@@ -18,7 +18,7 @@ ELSE()
    SET(GSSAPI_SERVER gssapi_server.cc)
    SET(GSSAPI_ERRMSG gssapi_errmsg.cc)
 
-   IF(APPLE)
+   IF(CMAKE_CXX_COMPILER_ID MATCHES "Clang")
      SET_SOURCE_FILES_PROPERTIES(
        ${GSSAPI_CLIENT} ${GSSAPI_SERVER} ${GSSAPI_ERRMSG}
        PROPERTY COMPILE_FLAGS "-Wno-deprecated-declarations")

plugin/auth_pam/testing/CMakeLists.txt

@@ -4,7 +4,7 @@ ADD_LIBRARY(pam_mariadb_mtr MODULE pam_mariadb_mtr.c)
 SET_TARGET_PROPERTIES (pam_mariadb_mtr PROPERTIES PREFIX "")
 TARGET_LINK_LIBRARIES(pam_mariadb_mtr pam)
 
-IF(APPLE)
+IF(CMAKE_C_COMPILER_ID MATCHES "Clang")
   SET_SOURCE_FILES_PROPERTIES(
     pam_mariadb_mtr.c
     PROPERTY COMPILE_FLAGS "-Wno-incompatible-pointer-types-discards-qualifiers")