stdbool.h: Update true and false expansions for C2x

C2x has changed the expansions of the true and false macros in
<stdbool.h> so that they have type _Bool (including in #if conditions,
i.e. an unsigned type in that context).  Use the new expansions in
GCC's <stdbool.h> for C2x.

See bug 82272 for related discussion (but this patch does *not*
implement the warning discussed there).

Note that it's possible there may be a further change to make bool,
true and false keywords (there was support in principle for that at
the April WG14 meeting).  But currently these expansions of type _Bool
are what C2x requires and there isn't actually a paper before WG14 at
present that would introduce the new keywords.

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/
2020-10-29  Joseph Myers  <joseph@codesourcery.com>

	* ginclude/stdbool.h [__STDC_VERSION__ > 201710L] (true, false):
	Define with type _Bool.

gcc/testsuite/
2020-10-29  Joseph Myers  <joseph@codesourcery.com>

	* gcc.dg/c11-bool-1.c, gcc.dg/c2x-bool-1.c, gcc.dg/c99-bool-4.c:
	New tests.

gcc/ginclude/stdbool.h

@@ -31,8 +31,13 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #ifndef __cplusplus
 
 #define bool	_Bool
+#if defined __STDC_VERSION__ && __STDC_VERSION__ > 201710L
+#define true	((_Bool)+1u)
+#define false	((_Bool)+0u)
+#else
 #define true	1
 #define false	0
+#endif
 
 #else /* __cplusplus */
 

gcc/testsuite/gcc.dg/c11-bool-1.c

@@ -0,0 +1,50 @@
+/* Test macro expansions in <stdbool.h> in C11.  */
+/* { dg-do run } */
+/* { dg-options "-std=c11 -pedantic-errors" } */
+
+#include <stdbool.h>
+
+#define str(x) xstr(x)
+#define xstr(x) #x
+
+extern void abort (void);
+extern void exit (int);
+extern int strcmp (const char *, const char *);
+
+#if false - 1 >= 0
+#error "false unsigned in #if"
+#endif
+
+#if false != 0
+#error "false not 0 in #if"
+#endif
+
+#if true - 2 >= 0
+#error "true unsigned in #if"
+#endif
+
+#if true != 1
+#error "true not 1 in #if"
+#endif
+
+int
+main (void)
+{
+  if (strcmp (str (bool), "_Bool") != 0)
+    abort ();
+  if (_Generic (true, int : 1) != 1)
+    abort ();
+  if (true != 1)
+    abort ();
+  if (strcmp (str (true), "1") != 0)
+    abort ();
+  if (_Generic (false, int : 1) != 1)
+    abort ();
+  if (false != 0)
+    abort ();
+  if (strcmp (str (false), "0") != 0)
+    abort ();
+  if (strcmp (str (__bool_true_false_are_defined), "1") != 0)
+    abort ();
+  exit (0);
+}

gcc/testsuite/gcc.dg/c2x-bool-1.c

@@ -0,0 +1,50 @@
+/* Test macro expansions in <stdbool.h> in C2x.  */
+/* { dg-do run } */
+/* { dg-options "-std=c2x -pedantic-errors" } */
+
+#include <stdbool.h>
+
+#define str(x) xstr(x)
+#define xstr(x) #x
+
+extern void abort (void);
+extern void exit (int);
+extern int strcmp (const char *, const char *);
+
+#if false - 1 < 0
+#error "false signed in #if"
+#endif
+
+#if false != 0
+#error "false not 0 in #if"
+#endif
+
+#if true - 2 < 0
+#error "true signed in #if"
+#endif
+
+#if true != 1
+#error "true not 1 in #if"
+#endif
+
+int
+main (void)
+{
+  if (strcmp (str (bool), "_Bool") != 0)
+    abort ();
+  if (_Generic (true, _Bool : 1) != 1)
+    abort ();
+  if (true != 1)
+    abort ();
+  if (strcmp (str (true), "((_Bool)+1u)") != 0)
+    abort ();
+  if (_Generic (false, _Bool : 1) != 1)
+    abort ();
+  if (false != 0)
+    abort ();
+  if (strcmp (str (false), "((_Bool)+0u)") != 0)
+    abort ();
+  if (strcmp (str (__bool_true_false_are_defined), "1") != 0)
+    abort ();
+  exit (0);
+}

gcc/testsuite/gcc.dg/c99-bool-4.c

@@ -0,0 +1,46 @@
+/* Test macro expansions in <stdbool.h> in C99.  */
+/* { dg-do run } */
+/* { dg-options "-std=c99 -pedantic-errors" } */
+
+#include <stdbool.h>
+
+#define str(x) xstr(x)
+#define xstr(x) #x
+
+extern void abort (void);
+extern void exit (int);
+extern int strcmp (const char *, const char *);
+
+#if false - 1 >= 0
+#error "false unsigned in #if"
+#endif
+
+#if false != 0
+#error "false not 0 in #if"
+#endif
+
+#if true - 2 >= 0
+#error "true unsigned in #if"
+#endif
+
+#if true != 1
+#error "true not 1 in #if"
+#endif
+
+int
+main (void)
+{
+  if (strcmp (str (bool), "_Bool") != 0)
+    abort ();
+  if (true != 1)
+    abort ();
+  if (strcmp (str (true), "1") != 0)
+    abort ();
+  if (false != 0)
+    abort ();
+  if (strcmp (str (false), "0") != 0)
+    abort ();
+  if (strcmp (str (__bool_true_false_are_defined), "1") != 0)
+    abort ();
+  exit (0);
+}