Simplify nanosleep Autoconf check (php#13490)

The nanosleep() is mostly found in libc, except on systems, such as
Solaris <= 10 or the discontinued OpenSolaris, it is in the rt library.

This checks if nanosleep() exists in the libc, then it checks if rt
library has nanosleep, prepends it to LIBS and defines the
HAVE_NANOSLEEP symbol with the template from the AC_CHECK_FUNCS.

Author: petk

configure.ac

@@ -620,7 +620,6 @@ usleep \
 utime \
 vasprintf \
 asprintf \
-nanosleep \
 memmem \
 memrchr \
 mempcpy \
@@ -638,8 +637,9 @@ AC_CHECK_HEADER([sys/procctl.h], [AC_CHECK_FUNCS([procctl])])
 
 AX_FUNC_WHICH_GETHOSTBYNAME_R
 
-dnl Some systems (like OpenSolaris) do not have nanosleep in libc.
-PHP_CHECK_FUNC_LIB(nanosleep, rt)
+dnl Some systems (Solaris 10) do not have nanosleep in libc.
+AC_CHECK_FUNCS([nanosleep],,
+  [AC_SEARCH_LIBS([nanosleep], [rt], [AC_DEFINE([HAVE_NANOSLEEP], [1])])])
 
 dnl Haiku does not have network api in libc.
 PHP_CHECK_FUNC_LIB(setsockopt, network)