[Buildroot] [PATCH 2/3] pkgconf: Add pkgconf system lib and include path

[Thomas Preston]

Hi Thomas,

On 01/10/2019 14:47, Thomas Petazzoni wrote:
> On Tue,  1 Oct 2019 13:41:31 +0100
> Thomas Preston <thomas.preston at codethink.co.uk> wrote:
> 
>> Buildroot does not reconfigure pkgconf system library and system include
>> dirs to STAGING_DIR. This means that pkgconf prints the sysroot system
>> library and system include dirs instead of letting the compiler handle
>> the logical sysroot. This breaks the -isystem compiler flag, as it
>> increases the priority of the system library and system include
>> directories. For example:
>>
>> 	$ output/host/bin/pkg-config --cflags glib-2.0
>> 	-Ioutput/host/bin/../x86_64-buildroot-linux-gnu/sysroot/usr/include/glib-2.0
>> 	-Ioutput/host/bin/../x86_64-buildroot-linux-gnu/sysroot/usr/lib/glib-2.0/include
>> 	-Ioutput/host/bin/../x86_64-buildroot-linux-gnu/sysroot/usr/include
>>
>> A header in `.../sysroot/usr/include` will be included before a header
>> in any directory specified with -isystem flags. Specifically, this
>> breaks the Chromium build system, which expects a C++ math.h in a
>> bundled LLVM C++ library, and gets a GNU C math.h instead.
>>
>> Fix this by telling pkgconf about the sysroot's system library and
>> system include directories, so that it doesn't accidentally print them.
>>
>> Signed-off-by: Thomas Preston <thomas.preston at codethink.co.uk>
> 
> I am wondering if this would not solve
> https://bugs.busybox.net/show_bug.cgi?id=11776 which is also related to
> -isystem causing problems. I think
> https://bugs.busybox.net/show_bug.cgi?id=12131 and
> https://bugs.busybox.net/show_bug.cgi?id=12231 are the same issue.
> 

I've commented on that first issue, but I don't think this will fix it.
The /usr/include in final -isystem should work because the priority order 
is:

	-I
	-isystem
	logical sysroot /usr/include

Our bug is where a header (GNU C math.h) in the logical sysroot is
included before the expected header (LLVM C++ math.h) in the -isystem
include, because pkgconf incorrectly returned a:

	-I.../sysroot/usr/include.