Extension should return a const char *.

include/grpc/support/subprocess.h

@@ -37,7 +37,7 @@
 typedef struct gpr_subprocess gpr_subprocess;
 
 /* .exe on windows, empty on unices */
-char *gpr_subprocess_binary_extension();
+const char *gpr_subprocess_binary_extension();
 
 gpr_subprocess *gpr_subprocess_create(int argc, char **argv);
 /* if subprocess has not been joined, kill it */

src/core/support/subprocess_posix.c

@@ -55,7 +55,7 @@ struct gpr_subprocess {
   int joined;
 };
 
-char *gpr_subprocess_binary_extension() { return ""; }
+const char *gpr_subprocess_binary_extension() { return ""; }
 
 gpr_subprocess *gpr_subprocess_create(int argc, char **argv) {
   gpr_subprocess *r;