Possible fix for www/firefox on NetBSD 8

[Tobias Nygren <tnn%NetBSD.org@localhost>]

NetBSD 8.2 users please test this change and check
if it results in a working browser? Thank you.

--- mozilla-common.mk   7 May 2020 10:14:16 -0000       1.166
+++ mozilla-common.mk   13 May 2020 22:08:00 -0000
@@ -248,6 +248,18 @@ PKG_CC=            ${PREFIX}/bin/clang
 PKG_CXX=       ${PREFIX}/bin/clang++
 BUILDLINK_DEPMETHOD.clang=     build
 .include "../../lang/clang/buildlink3.mk"
+.if !empty(MACHINE_PLATFORM:MNetBSD-8.*-*)
+.include "../../lang/gcc8/buildlink3.mk"
+CWRAPPERS_PREPEND.cxx+= \
+ -L${BUILDLINK_PREFIX.gcc8}/gcc8/lib \
+ ${COMPILER_RPATH_FLAG}${BUILDLINK_PREFIX.gcc8}/gcc8/lib \
+ -stdlib++-isystem \
+ ${BUILDLINK_PREFIX.gcc8}/gcc8/include/c++ \
+ -stdlib++-isystem \
+ ${BUILDLINK_PREFIX.gcc8}/gcc8/include/c++/${MACHINE_GNU_PLATFORM} \
+ -stdlib++-isystem \
+ ${BUILDLINK_PREFIX.gcc8}/gcc8/include/c++/backward
+.endif
 BUILDLINK_DEPMETHOD.rust=      build
 BUILDLINK_API_DEPENDS.rust+=   rust>=1.41.0
 .include "../../lang/rust/buildlink3.mk"