test: prevent incorrect quoting of paths

The path would previously get an extra leading space as the arguments
would be parsed when generating the final command to run.  Pretokenise
the arguments to permit proper quoting of the paths.  This avoids a
number of ignoring non-existent path warnings from clang.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@295511 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed