[Buildroot] [PATCH 1/2] package/Makefile.in should grab HOST_DIR headers using -isystem instead of -I.

[David Raeman <draeman@bbn.com>]

HOST_CFLAGS includes a search path for HOST_DIR/usr/include using -I.  When
HOST_CFLAGS is used by a package, these flags are passed to the compiler ahead
of flags passed by the package's internal make system.  If a package has a
header file with the same name as a header file in HOST_DIR, this causes the
toolchain to prefer the file from the system include directory because its -I
appears first on the command line.  I believe conflicts should prefer the file
provided by the package.  This can be accomplished by using -isystem, which is
more appropriate then -I for system-level include paths.

Real-world example: I need libfdt present in my HOST_DIR to install a patched
version of QEMU.  Meanwhile, the u-boot package provides its own copy of
libfdt.h that is modified from upstream.  If I have libfdt installed into
HOST_DIR, then host-uboot-tools fails to build because it grabs the libfdt.h
from the HOST_DIR area instead of using the patched version from its own
source tree.  This patch corrects this issue.

This assumes the -isystem flag is supported by the host compiler.

Signed-off-by: David Raeman <draeman@bbn.com>
---
 package/Makefile.in | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/package/Makefile.in b/package/Makefile.in
index afd5d3a..b0ef706 100644
--- a/package/Makefile.in
+++ b/package/Makefile.in
@@ -222,7 +222,7 @@ UNZIP := $(shell which unzip || type -p unzip) -q
 
 APPLY_PATCHES = support/scripts/apply-patches.sh $(if $(QUIET),-s)
 
-HOST_CPPFLAGS  = -I$(HOST_DIR)/usr/include
+HOST_CPPFLAGS  = -isystem $(HOST_DIR)/usr/include
 HOST_CFLAGS   ?= -O2
 HOST_CFLAGS   += $(HOST_CPPFLAGS)
 HOST_CXXFLAGS += $(HOST_CFLAGS)
-- 
2.7.4