[compiler-rt][Fuzzer] Fix the fuzzer test build

This fixes the issue introduced in r345765 which changed the way in
which the embedded libc++ is being built but omitted tests.

Differential Revision: https://reviews.llvm.org/D54058

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@346052 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed