Require sizeof(bool) == 1.

The C standard says that sizeof(bool) is implementation-defined, but we
know of no current systems where it is not 1.  The last known systems
seem to have been Apple macOS/PowerPC 10.5 and Microsoft Visual C++ 4,
both long defunct.

PostgreSQL has always required sizeof(bool) == 1 for the definition of
bool that it used, but previously it would define its own type if the
system-provided bool had a different size.  That was liable to cause
memory layout problems when interacting with system and third-party
libraries on (by now hypothetical) computers with wider _Bool, and now
C23 has introduced a new problem by making bool a built-in datatype
(like C++), so the fallback code doesn't even compile.  We could
probably work around that, but then we'd be writing new untested code
for a computer that doesn't exist.

Instead, delete the unreachable and C23-uncompilable fallback code, and
let existing static assertions fail if the system-provided bool is too
wide.  If we ever get a problem report from a real system, then it will
be time to figure out what to do about it in a way that also works on
modern compilers.

Note on C++: Previously we avoided including <stdbool.h> or trying to
define a new bool type in headers that might be included by C++ code.
These days we might as well just include <stdbool.h> unconditionally:
it should be visible to C++11 but do nothing, just as in C23.  We
already include <stdint.h> without C++ guards in c.h, and that falls
under the same C99-compatibility section of the C++11 standard as
<stdbool.h>, so let's remove the guards here too.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3198438.1731895163%40sss.pgh.pa.us

src/interfaces/ecpg/include/ecpg_config.h.in

@@ -6,6 +6,3 @@
 
 /* Define to 1 if `long long int' works and is 64 bits. */
 #undef HAVE_LONG_LONG_INT_64
-
-/* Define to 1 to use <stdbool.h> to define type bool. */
-#undef PG_USE_STDBOOL

src/interfaces/ecpg/include/ecpglib.h

@@ -7,6 +7,7 @@
 #ifndef _ECPGLIB_H
 #define _ECPGLIB_H
 
+#include <stdbool.h>
 #include <string.h>
 
 #include "ecpg_config.h"
@@ -14,35 +15,6 @@
 #include "libpq-fe.h"
 #include "sqlca.h"
 
-/*
- * This is a small extract from c.h since we don't want to leak all postgres
- * definitions into ecpg programs; but we need to know what bool is.
- */
-#ifndef __cplusplus
-
-#ifdef PG_USE_STDBOOL
-#include <stdbool.h>
-#else
-
-/*
- * We assume bool has been defined if true and false are.  This avoids
- * duplicate-typedef errors if this file is included after c.h.
- */
-#if !(defined(true) && defined(false))
-typedef unsigned char bool;
-#endif
-
-#ifndef true
-#define true	((bool) 1)
-#endif
-
-#ifndef false
-#define false	((bool) 0)
-#endif
-
-#endif							/* not PG_USE_STDBOOL */
-#endif							/* not C++ */
-
 
 #ifdef __cplusplus
 extern "C"

src/interfaces/ecpg/include/meson.build

@@ -5,7 +5,6 @@ ecpg_inc = include_directories('.')
 ecpg_conf_keys = [
   'HAVE_LONG_INT_64',
   'HAVE_LONG_LONG_INT_64',
-  'PG_USE_STDBOOL',
 ]
 
 ecpg_conf_data = configuration_data()