gcc handles -symbolic by passing -Bsymbolic through to ld. clang ignores
-symbolic and thus invokes ld without -Bsymbolic which leads to some symbols
not being properly linked in loader.efi. Fix this by using -Wl,-Bsymbolic which
passes -Bsymbolic to ld in both the gcc and clang cases.
Approved by: rpaulo