Merge mozilla-central to mozilla-inbound. a=merge CLOSED TREE

browser/config/mozconfigs/linux64/code-coverage

@@ -14,5 +14,4 @@ ac_add_options --enable-coverage
 export CFLAGS="--coverage"
 export CXXFLAGS="--coverage"
 export LDFLAGS="--coverage -L$topsrcdir/clang/lib/clang/7.0.0/lib/linux/"
-export RUSTFLAGS="-Ccodegen-units=1 -Zprofile -Zno-landing-pads"
 export LIBS="-lclang_rt.profile-x86_64"