cache the values of ghc_ge_XXX at configure-time

This avoids recomputing them via $(shell) each time make expands one
of these variables, which is very expensive (0.3s or so) on Windows.

configure.ac

@@ -715,6 +715,16 @@ if test "$WithGhc" != ""; then
   AC_SUBST(GhcMajVersion)dnl
   AC_SUBST(GhcMinVersion)dnl
   AC_SUBST(GhcPatchLevel)dnl
+  ghc_ge_504=`if test $(GhcCanonVersion) -ge 504; then echo YES; else echo NO; fi`
+  AC_SUBST(ghc_ge_504)dnl
+  ghc_ge_601=`if test $(GhcCanonVersion) -ge 601; then echo YES; else echo NO; fi`
+  AC_SUBST(ghc_ge_601)dnl
+  ghc_ge_602=`if test $(GhcCanonVersion) -ge 602; then echo YES; else echo NO; fi`
+  AC_SUBST(ghc_ge_602)dnl
+  ghc_ge_603=`if test $(GhcCanonVersion) -ge 603; then echo YES; else echo NO; fi`
+  AC_SUBST(ghc_ge_603)dnl
+  ghc_ge_605=`if test $(GhcCanonVersion) -ge 605; then echo YES; else echo NO; fi`
+  AC_SUBST(ghc_ge_605)dnl
 fi
 
 # Check whether this GHC has readline installed

mk/config.mk.in

@@ -833,11 +833,11 @@ GhcMajVersion	= @GhcMajVersion@
 GhcMinVersion	= @GhcMinVersion@
 
 # Some useful GHC version predicates:
-ghc_ge_504 = $(shell if (test $(GhcCanonVersion) -ge 504); then echo YES; else echo NO; fi)
-ghc_ge_601 = $(shell if (test $(GhcCanonVersion) -ge 601); then echo YES; else echo NO; fi)
-ghc_ge_602 = $(shell if (test $(GhcCanonVersion) -ge 602); then echo YES; else echo NO; fi)
-ghc_ge_603 = $(shell if (test $(GhcCanonVersion) -ge 603); then echo YES; else echo NO; fi)
-ghc_ge_605 = $(shell if (test $(GhcCanonVersion) -ge 605); then echo YES; else echo NO; fi)
+ghc_ge_504 = @ghc_ge_504@
+ghc_ge_601 = @ghc_ge_601@
+ghc_ge_602 = @ghc_ge_602@
+ghc_ge_603 = @ghc_ge_603@
+ghc_ge_605 = @ghc_ge_605@
 endif
 
 # Canonicalised ghc version number, used for easy (integer) version