Remove traces of Sun -lposix4.

This was a library on ancient Solaris systems, which was eventually
replaced by -lrt, itself now redundant on that OS.

Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Tristan Partin <tristan@neon.tech>
Discussion: https://postgr.es/m/CA%2BhUKGLLVx4drdvXats9PxH3eeB%2BE2NkJReJ%2BRGmaOpU%3D9rgEA%40mail.gmail.com

configure

@@ -12163,7 +12163,7 @@ return clock_gettime ();
   return 0;
 }
 _ACEOF
-for ac_lib in '' rt posix4; do
+for ac_lib in '' rt; do
   if test -z "$ac_lib"; then
     ac_res="none required"
   else

configure.ac

@@ -1285,7 +1285,7 @@ AC_SEARCH_LIBS(socket, [socket ws2_32])
 AC_SEARCH_LIBS(getopt_long, [getopt gnugetopt])
 AC_SEARCH_LIBS(shm_open, rt)
 AC_SEARCH_LIBS(shm_unlink, rt)
-AC_SEARCH_LIBS(clock_gettime, [rt posix4])
+AC_SEARCH_LIBS(clock_gettime, rt)
 # Cygwin:
 AC_SEARCH_LIBS(shmget, cygipc)
 # *BSD:

meson.build

@@ -2380,7 +2380,6 @@ rt_dep = cc.find_library('rt', required: false)
 dl_dep = cc.find_library('dl', required: false)
 
 util_dep = cc.find_library('util', required: false)
-posix4_dep = cc.find_library('posix4', required: false)
 
 getopt_dep = cc.find_library('getopt', required: false)
 gnugetopt_dep = cc.find_library('gnugetopt', required: false)
@@ -2414,7 +2413,7 @@ endif
 func_checks = [
   ['_configthreadlocale', {'skip': host_system != 'windows'}],
   ['backtrace_symbols', {'dependencies': [execinfo_dep]}],
-  ['clock_gettime', {'dependencies': [rt_dep, posix4_dep], 'define': false}],
+  ['clock_gettime', {'dependencies': [rt_dep], 'define': false}],
   ['copyfile'],
   # gcc/clang's sanitizer helper library provides dlopen but not dlsym, thus
   # when enabling asan the dlopen check doesn't notice that -ldl is actually