Unfortunately the patch broke
+FAIL: gcc.dg/pr20245-1.c (internal compiler error)
+FAIL: gcc.dg/pr20245-1.c (test for excess errors)
+FAIL: gcc.dg/pr28419.c (internal compiler error)
+FAIL: gcc.dg/pr28419.c (test for excess errors)
on some targets (and under valgrind on the rest of them).

Those functions don't have the opening { and so c_parser_compound_statement
returned error_mark_node before initializing *endlocp.
So, either we can initialize it in that case too:
--- gcc/c/c-parser.c    2020-03-20 22:09:39.659411721 +0100
+++ gcc/c/c-parser.c    2020-03-21 09:36:44.455705261 +0100
@@ -5611,6 +5611,8 @@ c_parser_compound_statement (c_parser *p
         if we have just prepared to enter a function body.  */
       stmt = c_begin_compound_stmt (true);
       c_end_compound_stmt (brace_loc, stmt, true);
+      if (endlocp)
+       *endlocp = brace_loc;
       return error_mark_node;
     }
   stmt = c_begin_compound_stmt (true);
or perhaps simpler initialize it to the function_start_locus at the
beginning and have those functions without { have function_start_locus ==
function_end_locus like the __GIMPLE functions (where propagating the
closing } seemed too difficult).

2020-03-23  Jakub Jelinek  <jakub@redhat.com>

	PR gcov-profile/94029
	PR c/94239
	* c-parser.c (c_parser_declaration_or_fndef): Initialize endloc to
	the function_start_locus location.  Don't do that afterwards for the
	__GIMPLE body parsing.