Suggest including <stdbool.h> for bool, true and false

Currently gcc suggests to use _Bool instead of bool and doesn't give
any suggestions when true or false are used, but undefined. This patch
makes it so that (for C99 or higher) a fixit hint is emitted to include
<stdbool.h>.

gcc/c-family/ChangeLog:

	* known-headers.cc (get_stdlib_header_for_name): Return
	"<stdbool.h>" for "bool", "true" or "false" when STDLIB_C and
	flag_isoc99.

gcc/testsuite/ChangeLog:

	* gcc.dg/spellcheck-stdbool.c: New test.

gcc/c-family/ChangeLog

+2020-05-22  Mark Wielaard  <mark@klomp.org>
+
+	* known-headers.cc (get_stdlib_header_for_name): Return
+	"<stdbool.h>" for "bool", "true" or "false" when STDLIB_C and
+	flag_isoc99.
+
 2020-05-20  Nathan Sidwell  <nathan@acm.org>
 
 	* c-common.c (try_to_locate_new_include_insertion_point): Revert change.

gcc/c-family/known-headers.cc

@@ -158,6 +158,14 @@ get_stdlib_header_for_name (const char *name, enum stdlib lib)
   for (size_t i = 0; i < num_hints; i++)
     if (strcmp (name, hints[i].name) == 0)
       return hints[i].header[lib];
+
+  /* Only for C99 and higher.  */
+  if (lib == STDLIB_C && flag_isoc99)
+    if (strcmp (name, "bool") == 0
+	|| strcmp (name, "true") == 0
+	|| strcmp (name, "false") == 0)
+      return "<stdbool.h>";
+
   return NULL;
 }
 

gcc/testsuite/ChangeLog

+2020-05-22  Mark Wielaard  <mark@klomp.org>
+
+	* gcc.dg/spellcheck-stdbool.c: New test.
+
 2020-05-22  Mark Wielaard  <mark@klomp.org>
 	* gcc.dg/analyzer/signal-exit.c: New testcase.

gcc/testsuite/gcc.dg/spellcheck-stdbool.c

+/* { dg-options "-std=c99" } */
+/* Missing <stdbool.h>.  */
+
+bool b; /* { dg-error "unknown type name 'bool'" } */
+/* { dg-message "'bool' is defined in header '<stdbool.h>'; did you forget to '#include <stdbool.h>'?" "" { target *-*-* } .-1 } */
+
+int test_true (void)
+{
+  return true; /* { dg-error "'true' undeclared" } */
+  /* { dg-message "'true' is defined in header '<stdbool.h>'; did you forget to '#include <stdbool.h>'?" "" { target *-*-* } .-1 } */
+}
+
+int test_false (void)
+{
+  return false; /* { dg-error "'false' undeclared" } */
+  /* { dg-message "'false' is defined in header '<stdbool.h>'; did you forget to '#include <stdbool.h>'?" "" { target *-*-* } .-1 } */
+}