Fix modules_install on RO nfs-exported trees.

Fixes http://bugzilla.kernel.org/show_bug.cgi?id=11355 by avoiding a
needless rebuild of the firmware/ihex2fw tool.
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

firmware/Makefile

@@ -146,15 +146,27 @@ $(patsubst %,$(obj)/%.gen.o, $(fw-external-y)): $(obj)/%.gen.o: $(fwdir)/%
 $(obj)/%: $(obj)/%.ihex | $(objtree)/$(obj)/$$(dir %)
 	$(call cmd,ihex)
 
+# Don't depend on ihex2fw if we're installing and it already exists.
+# Putting it after | in the dependencies doesn't seem sufficient when
+# we're installing after a cross-compile, because ihex2fw has dependencies
+# on stuff like /usr/lib/gcc/ppc64-redhat-linux/4.3.0/include/stddef.h and 
+# thus wants to be rebuilt. Which it can't be, if the prebuilt kernel tree
+# is exported read-only for someone to run 'make install'.
+ifeq ($(INSTALL):$(wildcard $(obj)/ihex2fw),install:$(obj)/ihex2fw)
+ihex2fw_dep :=
+else
+ihex2fw_dep := $(obj)/ihex2fw
+endif
+
 # .HEX is also Intel HEX, but where the offset and length in each record
 # is actually meaningful, because the firmware has to be loaded in a certain
 # order rather than as a single binary blob. Thus, we convert them into our
 # more compact binary representation of ihex records (<linux/ihex.h>)
-$(obj)/%.fw: $(obj)/%.HEX $(obj)/ihex2fw | $(objtree)/$(obj)/$$(dir %)
+$(obj)/%.fw: $(obj)/%.HEX $(ihex2fw_dep) | $(objtree)/$(obj)/$$(dir %)
 	$(call cmd,ihex2fw)
 
 # .H16 is our own modified form of Intel HEX, with 16-bit length for records.
-$(obj)/%.fw: $(obj)/%.H16 $(obj)/ihex2fw | $(objtree)/$(obj)/$$(dir %)
+$(obj)/%.fw: $(obj)/%.H16 $(ihex2fw_dep) | $(objtree)/$(obj)/$$(dir %)
 	$(call cmd,h16tofw)
 
 $(firmware-dirs):