package/libpam-tacplus: fix build without SSP

The following build failure without stack-protector occurs since commit
160f0e4b5f16 (package/libpam-tacplus: bump to version 1.7.0):

    cc1: warning: '-fstack-protector' not supported for this target
    In file included from libtac/lib/xstrncpy.c:36:
    libtac/lib/xstrncpy.c: In function 'xstrncpy':
    ./libtac/include/libtac.h:71:15: error: called object is not a function or function pointer
       71 | #define abort exit(EXIT_FAILURE)
          |               ^~~~

Since we are passing the appropriate SSP and fortify flags via our
toolchain wrapper, we need to tell the package not to add its own.
Upstream commit b1054ad8bb33 (Add '--disable-am-ldcflags' configure
option), available since version 1.4.1, has been added for "a
distribution to select its own C/LD flags" which is exactly our
situation.

So that's what we do: replace the ax cache variable by this new
configure flag.

Fixes:
 - http://autobuild.buildroot.org/results/cc8a7c5cca65e002d40a775f09e3c4577fbab5b7

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/libpam-tacplus/libpam-tacplus.mk

@@ -17,8 +17,6 @@ LIBPAM_TACPLUS_DEPENDENCIES = \
 # We're patching Makefile.am
 LIBPAM_TACPLUS_AUTORECONF = YES
 LIBPAM_TACPLUS_INSTALL_STAGING = YES
-LIBPAM_TACPLUS_CONF_ENV = \
-	ax_cv_check_cflags___fstack_protector_all=$(if $(BR2_TOOLCHAIN_HAS_SSP),yes,no)
-LIBPAM_TACPLUS_CONF_OPTS = --disable-werror
+LIBPAM_TACPLUS_CONF_OPTS = --disable-am-ldcflags --disable-werror
 
 $(eval $(autotools-package))