stdenv/setup.sh: Always run postPatch hook.

I'm not sure whether this was by intention, but so far postPatch hooks were
silently skipped whenever the patches list was empty. This change could possibly
change the build results of the following packages:

 * gcc
 * cmake (264)
 * systemtap
 * quemu-kvm

These packages all have in common that they have a postPatch hook and the
patches list can be empty when certain conditions are met.

Signed-off-by: aszlig <aszlig@redmoonstudios.org>

pkgs/stdenv/generic/setup.sh

@@ -530,8 +530,6 @@ unpackPhase() {
 patchPhase() {
     runHook prePatch
 
-    if [ -z "$patchPhase" -a -z "$patches" ]; then return; fi
-
     for i in $patches; do
         header "applying patch $i" 3
         local uncompress=cat

pkgs/stdenv/mingw/setup.sh

@@ -486,9 +486,7 @@ unpackPhase() {
 
 patchPhase() {
     runHook prePatch
-    
-    if test -z "$patchPhase" -a -z "$patches"; then return; fi
-    
+
     for i in $patches; do
         header "applying patch $i" 3
         local uncompress=cat