kbuild: fix ia64 breakage after introducing make -rR

kbuild used $ยค(*F to get filename of target without extension.
This was used in several places all over kbuild, but introducing
make -rR broke his for all cases where we specified full path to
target/prerequsite. It is assumed that make -rR disables old style
suffix-rules which is why is suddenly failed.

ia64 was impacted by this change because several div* routines in
arch/ia64/lib are build using explicit paths and then kbuild failed.

Thanks to David Mosberger-Tang <David.Mosberger@acm.org> for an explanation
what was the root-cause and for testing on ia64.

This patch also fixes two uses of $(*F) in arch/um

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/Makefile.host b/scripts/Makefile.host
index 2b066d1..18ecd4d 100644
--- a/scripts/Makefile.host
+++ b/scripts/Makefile.host
@@ -80,8 +80,10 @@
 #####
 # Handle options to gcc. Support building with separate output directory
 
-_hostc_flags   = $(HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   $(HOSTCFLAGS_$(*F).o)
-_hostcxx_flags = $(HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) $(HOSTCXXFLAGS_$(*F).o)
+_hostc_flags   = $(HOSTCFLAGS)   $(HOST_EXTRACFLAGS)   \
+                 $(HOSTCFLAGS_$(basetarget).o)
+_hostcxx_flags = $(HOSTCXXFLAGS) $(HOST_EXTRACXXFLAGS) \
+                 $(HOSTCXXFLAGS_$(basetarget).o)
 
 ifeq ($(KBUILD_SRC),)
 __hostc_flags	= $(_hostc_flags)