Move clock/timer fun checks to RTS configure

Actual library check (which will set the Cabal flag) is left in the
top-level configure for now.

Progress towards #17191

configure.ac

@@ -1010,16 +1010,8 @@ FP_VISIBILITY_HIDDEN
 FP_MUSTTAIL
 
 dnl ** check for librt
-AC_CHECK_LIB([rt], [clock_gettime])
-AC_CHECK_LIB([rt], [clock_gettime], HaveLibrt=YES, HaveLibrt=NO)
-if test $HaveLibrt = YES
-then
-  AC_SUBST([UseLibrt],[YES])
-else
-  AC_SUBST([UseLibrt],[NO])
-fi
-AC_CHECK_FUNCS(clock_gettime timer_settime)
-FP_CHECK_TIMER_CREATE
+AC_CHECK_LIB([rt], [clock_gettime], UseLibrt=YES, UseLibrt=NO)
+AC_SUBST([UseLibrt])
 
 FP_CHECK_PTHREAD_LIB
 AC_SUBST([UseLibpthread])

rts/configure.ac

@@ -33,6 +33,10 @@ GHC_CONVERT_PLATFORM_PARTS([host], [Host])
 FPTOOLS_SET_PLATFORM_VARS([host], [Host])
 FPTOOLS_SET_HASKELL_PLATFORM_VARS([Host])
 
+dnl ** check for librt
+AC_CHECK_FUNCS(clock_gettime timer_settime)
+FP_CHECK_TIMER_CREATE
+
 dnl ** check for Apple's "interesting" long double compatibility scheme
 AC_MSG_CHECKING(for printf\$LDBLStub)
 AC_LINK_IFELSE([AC_LANG_CALL([], [printf\$LDBLStub])],