MDEV-19208 mariadb.pc: install into libdir

The .pc file installed by mariadb mentions archful directories and
therefore must be archful itself.

This fixes MDEV-14340.

debian/libmariadb-dev.install

@@ -5,5 +5,5 @@ usr/lib/*/libmysqlclient.so
 usr/lib/*/libmariadbclient.so
 usr/lib/*/libmariadbclient.a
 usr/lib/*/libmysqlservices.a
+usr/lib/*/pkgconfig/mariadb.pc
 usr/share/aclocal/mysql.m4
-usr/share/pkgconfig/mariadb.pc

support-files/CMakeLists.txt

@@ -100,7 +100,7 @@ IF(UNIX)
   ENDIF()
 
   CONFIGURE_FILE(mariadb.pc.in ${CMAKE_CURRENT_BINARY_DIR}/mariadb.pc @ONLY)
-  INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/mariadb.pc DESTINATION ${INSTALL_SHAREDIR}/pkgconfig COMPONENT Development)
+  INSTALL(FILES ${CMAKE_CURRENT_BINARY_DIR}/mariadb.pc DESTINATION ${INSTALL_LIBDIR}/pkgconfig COMPONENT Development)
 
   INSTALL(FILES mysql.m4 DESTINATION ${INSTALL_SHAREDIR}/aclocal COMPONENT Development)