Fix windows breakage (fallout from 34f7e9a3)

Signed-off-by: Austin Seipp <austin@well-typed.com>
(cherry picked from commit 0567a313)

aclocal.m4

@@ -452,6 +452,7 @@ AC_DEFUN([FP_SETTINGS],
         mingw_bin_prefix=mingw/bin/
         SettingsCCompilerCommand="\$topdir/../${mingw_bin_prefix}gcc.exe"
         SettingsHaskellCPPCommand="\$topdir/../${mingw_bin_prefix}gcc.exe"
+        SettingsHaskellCPPFlags="$HaskellCPPArgs"
         SettingsLdCommand="\$topdir/../${mingw_bin_prefix}ld.exe"
         SettingsArCommand="\$topdir/../${mingw_bin_prefix}ar.exe"
         SettingsPerlCommand='$topdir/../perl/perl.exe'

configure.ac

@@ -493,10 +493,7 @@ AC_ARG_WITH(hs-cpp,
     fi
 ],
 [
-    if test "$HostOS" != "mingw32"
-    then
         HaskellCPPCmd=$WhatGccIsCalled
-    fi
 ]
 )