package/squid: needs atomic

Since https://github.com/squid-cache/squid/commit/4b0f89121135aae68fbaf2aa33b5fb2e0da66d3e
squid tries to find if latomic is needed through:
AC_SEARCH_LIBS([__atomic_load_8],[atomic],[ATOMICLIB="-latomic"],[])

However, this can fails on:
configure:21147: /home/fabrice/buildroot/output/host/bin/arc-buildroot-linux-gnu-g++ -o conftest -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -matomic -Os   -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -g conftest.cpp -latomic   >&5
conftest.cpp:55:6: error: new declaration 'char __atomic_load_8()' ambiguates built-in declaration 'long long unsigned int __atomic_load_8(const volatile void*, int)' [-fpermissive]
 char __atomic_load_8 ();
      ^~~~~~~~~~~~~~~
conftest.cpp: In function 'int main()':
conftest.cpp:59:25: error: too few arguments to function 'long long unsigned int __atomic_load_8(const volatile void*, int)'
 return __atomic_load_8 ();

So add -latomic to LIBS if BR2_TOOLCHAIN_HAS_LIBATOMIC is set

Fixes:
 - http://autobuild.buildroot.org/results/13082cea836a12ac8bf85cbdb53a56a5d30c70b1

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/squid/Config.in

@@ -1,10 +1,12 @@
 comment "squid needs a toolchain w/ C++, gcc >= 4.8 not affected by bug 64735"
 	depends on BR2_USE_MMU
+	depends on BR2_TOOLCHAIN_HAS_ATOMIC
 	depends on BR2_TOOLCHAIN_HAS_GCC_BUG_64735 || \
 		!BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_GCC_AT_LEAST_4_8
 
 config BR2_PACKAGE_SQUID
 	bool "squid"
+	depends on BR2_TOOLCHAIN_HAS_ATOMIC
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on !BR2_TOOLCHAIN_HAS_GCC_BUG_64735 # std::current_exception
 	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_4_8 # C++11

package/squid/squid.mk

@@ -38,6 +38,10 @@ SQUID_CONF_OPTS = \
 	--with-swapdir=/var/cache/squid/ \
 	--with-default-user=squid
 
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+SQUID_CONF_ENV += LIBS=-latomic
+endif
+
 ifeq ($(BR2_PACKAGE_LIBKRB5),y)
 SQUID_CONF_OPTS += --with-mit-krb5
 SQUID_DEPENDENCIES += libkrb5