[msan] Fix GCC warnings.

warning: ISO C99 requires rest arguments to be used [enabled by default]
 INTERCEPTOR(char *, dlerror) {

warning: invoking macro INTERCEPTOR argument 3: empty macro arguments are undefined in ISO C90 and ISO C++98 [enabled by default]



git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@199873 91177308-0d34-0410-b5e6-96231b3b80d8