[compiler-rt] Appending COMPILER_RT_LIBCXX_PATH -isystem include for xray (3)
[compiler-rt] Appending COMPILER_RT_LIBCXX_PATH -isystem include for xray (3)

Third landing attempt: Added "if (HAVE_LIBCXX)" to keep Green Dragon green.

Haven't found a better way to pass the libcxx include path for building
compiler-rt with libcxx; this seems to be missing only for xray.

Differential Revision: https://reviews.llvm.org/D65307



git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@367962 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt