package/linux-pam: link with -latomic when needed

Fix the following build failure raised since bump to version 1.5.3 in
commit f8147e27cdac8f998ec6644a09ce4e8d62b6433c and
https://github.com/linux-pam/linux-pam/commit/a35e092e24ee7632346a0e1b4a203c04d4cd2c62:

/home/buildroot/autobuild/instance-3/output-1/host/opt/ext-toolchain/bin/../lib/gcc/sparc-buildroot-linux-uclibc/11.3.0/../../../../sparc-buildroot-linux-uclibc/bin/ld: .libs/pam_keyinit.o: in function `pam_sm_open_session':
pam_keyinit.c:(.text+0x824): undefined reference to `__atomic_fetch_add_4'

Fixes:
 - http://autobuild.buildroot.org/results/52c51b5ad5930ed783b88fb33932297379fd4429

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit f1a47904b635c3c4c3b5656e58c0c575c1674993)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/linux-pam/linux-pam.mk

@@ -21,9 +21,14 @@ LINUX_PAM_DEPENDENCIES = flex host-flex host-pkgconf \
 	$(TARGET_NLS_DEPENDENCIES)
 LINUX_PAM_LICENSE = BSD-3-Clause
 LINUX_PAM_LICENSE_FILES = Copyright
-LINUX_PAM_MAKE_OPTS += LIBS=$(TARGET_NLS_LIBS)
+LINUX_PAM_LIBS = $(TARGET_NLS_LIBS)
+LINUX_PAM_MAKE_OPTS += LIBS="$(LINUX_PAM_LIBS)"
 LINUX_PAM_CPE_ID_VENDOR = linux-pam
 
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+LINUX_PAM_LIBS += -latomic
+endif
+
 ifeq ($(BR2_PACKAGE_LIBSELINUX),y)
 LINUX_PAM_CONF_OPTS += --enable-selinux
 LINUX_PAM_DEPENDENCIES += libselinux