Revert "Replace pg_restrict by standard restrict"

This reverts commit f0f2c0c1ae.

The original problem that led to the use of pg_restrict was that MSVC
couldn't handle plain restrict, and defining it to something else
would conflict with its __declspec(restrict) that is used in system
header files.  In C11 mode, this is no longer a problem, as MSVC
handles plain restrict.  This led to the commit to replace pg_restrict
with restrict.  But this did not take C++ into account.  Standard C++
does not have restrict, so we defined it as something else (for
example, MSVC supports __restrict).  But this then again conflicts
with __declspec(restrict) in system header files.  So we have to
revert this attempt.  The comments are updated to clarify that the
reason for this is now C++ only.

Reported-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://www.postgresql.org/message-id/CAGECzQRoD7chJP1-dneSrhxUJv%2BBRcigoGOO4UwGzaShLot2Yw%40mail.gmail.com

src/include/c.h

@@ -108,12 +108,6 @@
 #define inline
 #endif
 
-/*
- * Previously used PostgreSQL-specific spelling, for backward compatibility
- * for extensions.
- */
-#define pg_restrict restrict
-
 /*
  * Attribute macros
  *

src/include/common/logging.h

@@ -93,10 +93,10 @@ void		pg_logging_set_pre_callback(void (*cb) (void));
 void		pg_logging_set_locus_callback(void (*cb) (const char **filename, uint64 *lineno));
 
 void		pg_log_generic(enum pg_log_level level, enum pg_log_part part,
-						   const char *restrict fmt,...)
+						   const char *pg_restrict fmt,...)
 			pg_attribute_printf(3, 4);
 void		pg_log_generic_v(enum pg_log_level level, enum pg_log_part part,
-							 const char *restrict fmt, va_list ap)
+							 const char *pg_restrict fmt, va_list ap)
 			pg_attribute_printf(3, 0);
 
 /*

src/include/common/string.h

@@ -25,7 +25,7 @@ typedef struct PromptInterruptContext
 
 /* functions in src/common/string.c */
 extern bool pg_str_endswith(const char *str, const char *end);
-extern int	strtoint(const char *restrict str, char **restrict endptr,
+extern int	strtoint(const char *pg_restrict str, char **pg_restrict endptr,
 					 int base);
 extern char *pg_clean_ascii(const char *str, int alloc_flags);
 extern int	pg_strip_crlf(char *str);

src/include/libpq/pqformat.h

@@ -34,7 +34,7 @@ extern void pq_sendfloat8(StringInfo buf, float8 f);
  * Append a [u]int8 to a StringInfo buffer, which already has enough space
  * preallocated.
  *
- * The use of restrict allows the compiler to optimize the code based on
+ * The use of pg_restrict allows the compiler to optimize the code based on
  * the assumption that buf, buf->len, buf->data and *buf->data don't
  * overlap. Without the annotation buf->len etc cannot be kept in a register
  * over subsequent pq_writeintN calls.
@@ -43,7 +43,7 @@ extern void pq_sendfloat8(StringInfo buf, float8 f);
  * overly picky and demanding a * before a restrict.
  */
 static inline void
-pq_writeint8(StringInfoData *restrict buf, uint8 i)
+pq_writeint8(StringInfoData *pg_restrict buf, uint8 i)
 {
 	uint8		ni = i;
 
@@ -57,7 +57,7 @@ pq_writeint8(StringInfoData *restrict buf, uint8 i)
  * preallocated.
  */
 static inline void
-pq_writeint16(StringInfoData *restrict buf, uint16 i)
+pq_writeint16(StringInfoData *pg_restrict buf, uint16 i)
 {
 	uint16		ni = pg_hton16(i);
 
@@ -71,7 +71,7 @@ pq_writeint16(StringInfoData *restrict buf, uint16 i)
  * preallocated.
  */
 static inline void
-pq_writeint32(StringInfoData *restrict buf, uint32 i)
+pq_writeint32(StringInfoData *pg_restrict buf, uint32 i)
 {
 	uint32		ni = pg_hton32(i);
 
@@ -85,7 +85,7 @@ pq_writeint32(StringInfoData *restrict buf, uint32 i)
  * preallocated.
  */
 static inline void
-pq_writeint64(StringInfoData *restrict buf, uint64 i)
+pq_writeint64(StringInfoData *pg_restrict buf, uint64 i)
 {
 	uint64		ni = pg_hton64(i);
 
@@ -105,7 +105,7 @@ pq_writeint64(StringInfoData *restrict buf, uint64 i)
  * sent to the frontend.
  */
 static inline void
-pq_writestring(StringInfoData *restrict buf, const char *restrict str)
+pq_writestring(StringInfoData *pg_restrict buf, const char *pg_restrict str)
 {
 	int			slen = strlen(str);
 	char	   *p;

src/include/pg_config.h.in

@@ -786,6 +786,10 @@
 #undef inline
 #endif
 
+/* Define to keyword to use for C99 restrict support, or to nothing if not
+   supported */
+#undef pg_restrict
+
 /* Define to the equivalent of the C99 'restrict' keyword, or to
    nothing if this is not supported.  Do not define if restrict is
    supported directly.  */