[PATCH] common.mk: tweak rules to workaround make-3.80 bugs

[Mike Frysinger]

I got some reports from people who use make-3.80 that mtd-utils wasn't
building correctly the first time.  Turns out that older versions of make
misbehave with pattern rules and full paths.  So I've tweaked the code a
little to work with make-3.80 and make-3.81 (the latest release).

Also, I added a small optimization to avoid running `mkdir` when building
in-tree.

Signed-off-by: Mike Frysinger <vapier at gentoo.org>
---
 common.mk |    5 ++++-
 1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/common.mk b/common.mk
index 5dd21ab..77d28bf 100644
--- a/common.mk
+++ b/common.mk
@@ -19,6 +19,7 @@ else
   BUILDDIR := $(PWD)/$(CROSS:-=)
 endif
 endif
+override BUILDDIR := $(patsubst %/,%,$(BUILDDIR))
 
 override TARGETS := $(addprefix $(BUILDDIR)/,$(TARGETS))
 
@@ -33,7 +34,7 @@ clean:: $(SUBDIRS_CLEAN)
 
 install:: $(TARGETS) $(SUBDIRS_INSTALL)
 
-$(BUILDDIR)/%: $(BUILDDIR)/%.o
+%: %.o
 	$(CC) $(CFLAGS) $(LDFLAGS) $(LDFLAGS_$(notdir $@)) -g -o $@ $^ $(LDLIBS) $(LDLIBS_$(notdir $@))
 
 $(BUILDDIR)/%.a:
@@ -41,7 +42,9 @@ $(BUILDDIR)/%.a:
 	$(RANLIB) $@
 
 $(BUILDDIR)/%.o: %.c
+ifneq ($(BUILDDIR),$(CURDIR))
 	mkdir -p $(dir $@)
+endif
 	$(CC) $(CPPFLAGS) $(CFLAGS) -c -o $@ $< -g -Wp,-MD,$(BUILDDIR)/.$(<F).dep
 
 subdirs_%:
-- 
1.6.1