Find AppArmor library with pkgconf (#13644)

The AppArmor library has had pkg-config/pkgconf integration since its
early versions (2012), when it was integrated from the libaalogparse
into the AppArmor project. To ease this change, the check without
pkgconf is executed in case the libapparmor.pc file is not found on the
system.

A sanity check also covers cases where the library path is overriden:
  /configure --enable-fpm --with-fpm-apparmor \
    APPARMOR_CFLAGS=-I/path/to/libapparmor \
    APPARMOR_LIBS="-L/path/to/libapparmor -lapparmor"

This also removes the redundant symbol HAVE_SYS_APPARMOR_H since the
sys/apparmor.h header is considered a required part of the AppArmor
library package.

Author: petk

sapi/fpm/config.m4

@@ -515,13 +515,21 @@ if test "$PHP_FPM" != "no"; then
   fi
 
   if test "x$PHP_FPM_APPARMOR" != "xno" ; then
-    AC_CHECK_HEADERS([sys/apparmor.h])
-    AC_CHECK_LIB(apparmor, aa_change_profile, [
-      PHP_ADD_LIBRARY(apparmor)
-      AC_DEFINE(HAVE_APPARMOR, 1, [ AppArmor confinement available ])
-    ],[
-      AC_MSG_ERROR(libapparmor required but not found)
-    ])
+    PKG_CHECK_MODULES([APPARMOR], [libapparmor], [
+      PHP_EVAL_LIBLINE([$APPARMOR_LIBS])
+      PHP_EVAL_INCLINE([$APPARMOR_CFLAGS])
+    ],
+      [AC_CHECK_LIB([apparmor], [aa_change_profile],
+        [PHP_ADD_LIBRARY([apparmor])],
+        [AC_MSG_ERROR([libapparmor required but not found.])])])
+
+    dnl Sanity check.
+    CFLAGS_save="$CFLAGS"
+    CFLAGS="$INCLUDES $CFLAGS"
+    AC_CHECK_HEADER([sys/apparmor.h],
+      [AC_DEFINE([HAVE_APPARMOR], [1], [AppArmor confinement available])],
+      [AC_MSG_ERROR([Required sys/apparmor.h not found.])])
+    CFLAGS="$CFLAGS_save"
   fi
 
   if test "x$PHP_FPM_SELINUX" != "xno" ; then