travis: use external lld for linux

Author: andrewrk

ci/travis_linux_script

@@ -9,7 +9,7 @@ which $CXX
 echo $PATH
 mkdir build
 cd build
-cmake .. -DCMAKE_INSTALL_PREFIX=$(pwd) -DZIG_LIBC_LIB_DIR=$(dirname $($CC -print-file-name=crt1.o)) -DZIG_LIBC_INCLUDE_DIR=$(echo -n | $CC -E -x c - -v 2>&1 | grep -B1 "End of search list." | head -n1 | cut -c 2- | sed "s/ .*//") -DZIG_LIBC_STATIC_LIB_DIR=$(dirname $($CC -print-file-name=crtbegin.o))
+cmake .. -DCMAKE_INSTALL_PREFIX=$(pwd) -DZIG_LIBC_LIB_DIR=$(dirname $($CC -print-file-name=crt1.o)) -DZIG_LIBC_INCLUDE_DIR=$(echo -n | $CC -E -x c - -v 2>&1 | grep -B1 "End of search list." | head -n1 | cut -c 2- | sed "s/ .*//") -DZIG_LIBC_STATIC_LIB_DIR=$(dirname $($CC -print-file-name=crtbegin.o)) -DZIG_FORCE_EXTERNAL_LLD=ON
 make VERBOSE=1
 make install
 ./zig build --build-file ../build.zig test