Remove configure probe for clock_gettime.

clock_gettime() is in SUSv2 and all targeted Unix systems have it.
Remove a chunk of fallback code for old Unix is no longer reachable on
modern systems, and untested as of the retirement of build farm animal
prairiedog.

There is no need to retain a HAVE_CLOCK_GETTIME macro here, because it
is already used in a context with Unix and Windows code paths.

Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/CA+hUKGJ3LHeP9w5Fgzdr4G8AnEtJ=z=p6hGDEm4qYGEUX5B6fQ@mail.gmail.com

configure

@@ -16039,7 +16039,7 @@ fi
 LIBS_including_readline="$LIBS"
 LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
-for ac_func in backtrace_symbols clock_gettime copyfile fdatasync getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
+for ac_func in backtrace_symbols copyfile fdatasync getifaddrs getpeerucred inet_pton kqueue mbstowcs_l memset_s posix_fallocate ppoll pthread_is_threaded_np setproctitle setproctitle_fast strchrnul strsignal syncfs sync_file_range uselocale wcstombs_l
 do :
   as_ac_var=`$as_echo "ac_cv_func_$ac_func" | $as_tr_sh`
 ac_fn_c_check_func "$LINENO" "$ac_func" "$as_ac_var"

configure.ac

@@ -1791,7 +1791,6 @@ LIBS=`echo "$LIBS" | sed -e 's/-ledit//g' -e 's/-lreadline//g'`
 
 AC_CHECK_FUNCS(m4_normalize([
 	backtrace_symbols
-	clock_gettime
 	copyfile
 	fdatasync
 	getifaddrs

src/include/pg_config.h.in

@@ -83,9 +83,6 @@
 /* Define to 1 if you have the `BIO_meth_new' function. */
 #undef HAVE_BIO_METH_NEW
 
-/* Define to 1 if you have the `clock_gettime' function. */
-#undef HAVE_CLOCK_GETTIME
-
 /* Define to 1 if your compiler handles computed gotos. */
 #undef HAVE_COMPUTED_GOTO
 

src/include/portability/instr_time.h

@@ -57,8 +57,6 @@
 
 #ifndef WIN32
 
-#ifdef HAVE_CLOCK_GETTIME
-
 /* Use clock_gettime() */
 
 #include <time.h>
@@ -141,72 +139,6 @@ typedef struct timespec instr_time;
 #define INSTR_TIME_GET_MICROSEC(t) \
 	(((uint64) (t).tv_sec * (uint64) 1000000) + (uint64) ((t).tv_nsec / 1000))
 
-#else							/* !HAVE_CLOCK_GETTIME */
-
-/* Use gettimeofday() */
-
-#include <sys/time.h>
-
-typedef struct timeval instr_time;
-
-#define INSTR_TIME_IS_ZERO(t)	((t).tv_usec == 0 && (t).tv_sec == 0)
-
-#define INSTR_TIME_SET_ZERO(t)	((t).tv_sec = 0, (t).tv_usec = 0)
-
-#define INSTR_TIME_SET_CURRENT(t)	gettimeofday(&(t), NULL)
-
-#define INSTR_TIME_ADD(x,y) \
-	do { \
-		(x).tv_sec += (y).tv_sec; \
-		(x).tv_usec += (y).tv_usec; \
-		/* Normalize */ \
-		while ((x).tv_usec >= 1000000) \
-		{ \
-			(x).tv_usec -= 1000000; \
-			(x).tv_sec++; \
-		} \
-	} while (0)
-
-#define INSTR_TIME_SUBTRACT(x,y) \
-	do { \
-		(x).tv_sec -= (y).tv_sec; \
-		(x).tv_usec -= (y).tv_usec; \
-		/* Normalize */ \
-		while ((x).tv_usec < 0) \
-		{ \
-			(x).tv_usec += 1000000; \
-			(x).tv_sec--; \
-		} \
-	} while (0)
-
-#define INSTR_TIME_ACCUM_DIFF(x,y,z) \
-	do { \
-		(x).tv_sec += (y).tv_sec - (z).tv_sec; \
-		(x).tv_usec += (y).tv_usec - (z).tv_usec; \
-		/* Normalize after each add to avoid overflow/underflow of tv_usec */ \
-		while ((x).tv_usec < 0) \
-		{ \
-			(x).tv_usec += 1000000; \
-			(x).tv_sec--; \
-		} \
-		while ((x).tv_usec >= 1000000) \
-		{ \
-			(x).tv_usec -= 1000000; \
-			(x).tv_sec++; \
-		} \
-	} while (0)
-
-#define INSTR_TIME_GET_DOUBLE(t) \
-	(((double) (t).tv_sec) + ((double) (t).tv_usec) / 1000000.0)
-
-#define INSTR_TIME_GET_MILLISEC(t) \
-	(((double) (t).tv_sec * 1000.0) + ((double) (t).tv_usec) / 1000.0)
-
-#define INSTR_TIME_GET_MICROSEC(t) \
-	(((uint64) (t).tv_sec * (uint64) 1000000) + (uint64) (t).tv_usec)
-
-#endif							/* HAVE_CLOCK_GETTIME */
-
 #else							/* WIN32 */
 
 /* Use QueryPerformanceCounter() */

src/tools/msvc/Solution.pm

@@ -228,7 +228,6 @@ sub GenerateFiles
 		HAVE_BACKTRACE_SYMBOLS     => undef,
 		HAVE_BIO_GET_DATA          => undef,
 		HAVE_BIO_METH_NEW          => undef,
-		HAVE_CLOCK_GETTIME         => undef,
 		HAVE_COMPUTED_GOTO         => undef,
 		HAVE_COPYFILE              => undef,
 		HAVE_COPYFILE_H            => undef,