package/squid: needs gcc and host gcc >= 8

cf_gen.cc is compiled by host compiler and unconditionally uses auto
since bump to version 6.6 in commit
c13199c9326fa2daa574f08ec8fc063a48d0eb06 and
https://github.com/squid-cache/squid/commit/09835feb258c3058d028918e36d959dccb3f7496
resulting in the following build failure with host gcc < 8:

/usr/bin/g++ -O2 -I/home/buildroot/autobuild/run/instance-1/output-1/host/include -o cf_gen ./cf_gen.cc -I. -I../include/ -I../src
./cf_gen.cc: In function 'int main(int, char**)':
./cf_gen.cc:268:63: error: forming reference to void
                     auto &newEntry = entries.emplace_back(name);
                                                               ^

So add a dependency on host gcc >= 8 and gcc >= 8 as advocated by
upstream in
https://github.com/squid-cache/squid/blob/9d3433c4ac6cd547c10cf298b8a5e61a463fb753/doc/release-notes/release-6.sgml.in:

  This release adds a dependency on C++17 support in any compiler used to build Squid.
  GCC 8+ and Clang 8+ support C++17.

While at it, drop BR2_TOOLCHAIN_HAS_GCC_BUG_64735 which is always false
with gcc >= 7

Fixes: c13199c9326fa2daa574f08ec8fc063a48d0eb06
 - http://autobuild.buildroot.org/results/f1766d1a3b2ce7745fa23cdeae1101806cd97aea

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
(cherry picked from commit b8db5c466046dc2f3d9c411e6c9924667dd1a40c)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/squid/Config.in

@@ -1,18 +1,18 @@
-comment "squid needs a toolchain w/ C++, threads, gcc >= 7 not affected by bug 64735"
+comment "squid needs a toolchain w/ C++, threads, gcc >= 8, host gcc >= 8"
 	depends on BR2_USE_MMU
 	depends on BR2_TOOLCHAIN_HAS_ATOMIC
-	depends on BR2_TOOLCHAIN_HAS_GCC_BUG_64735 || \
-		!BR2_INSTALL_LIBSTDCPP || \
+	depends on !BR2_INSTALL_LIBSTDCPP || \
 		!BR2_TOOLCHAIN_HAS_THREADS || \
-		!BR2_TOOLCHAIN_GCC_AT_LEAST_7
+		!BR2_TOOLCHAIN_GCC_AT_LEAST_8 || \
+		!BR2_HOST_GCC_AT_LEAST_8
 
 config BR2_PACKAGE_SQUID
 	bool "squid"
 	depends on BR2_TOOLCHAIN_HAS_ATOMIC
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_HAS_THREADS
-	depends on !BR2_TOOLCHAIN_HAS_GCC_BUG_64735 # std::current_exception
-	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_7 # C++17
+	depends on BR2_TOOLCHAIN_GCC_AT_LEAST_8 # C++17
+	depends on BR2_HOST_GCC_AT_LEAST_8 # C++17
 	# needs fork()
 	depends on BR2_USE_MMU
 	select BR2_PACKAGE_LIBCAP