Merge pull request #12845 from ncteisen/fix-posix-build

Fix compilation on Mac
diff --git a/src/core/lib/support/log_posix.cc b/src/core/lib/support/log_posix.cc
index 38a136e..29530c8 100644
--- a/src/core/lib/support/log_posix.cc
+++ b/src/core/lib/support/log_posix.cc
@@ -58,7 +58,7 @@
 }
 
 extern "C" void gpr_default_log(gpr_log_func_args *args) {
-  char *final_slash;
+  const char *final_slash;
   const char *display_file;
   char time_buffer[64];
   time_t timer;