From bbb03794def326c2e8ad2de523c5a61a4c8cb464 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C3=B6rg=20Krause?= <joerg.krause@embedded.rocks>
Date: Thu, 22 Sep 2016 00:58:58 +0200
Subject: [PATCH] Remove replacing -I with -isystem
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Building OLA with a GCC 6 cross-toolchain fails:

```
/usr/bin/arm-linux-g++ -DHAVE_CONFIG_H -I.   -D_LARGEFILE_SOURCE
-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -I./include -I./include
-Wall -Wformat -W -isystem
/usr/arm-buildroot-linux-gnueabihf/sysroot/usr/include -pthread
-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os
-pthread -c -o libs/acn/e131_transmit_test.o
libs/acn/e131_transmit_test.cpp
/usr/bin/arm-linux-g++ -DHAVE_CONFIG_H -I.   -D_LARGEFILE_SOURCE
-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 -I./include -I./include
-Wall -Wformat -W -isystem
/usr/arm-buildroot-linux-gnueabihf/sysroot/usr/include -pthread
-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64  -Os
-pthread -c -o libs/acn/E131TestFramework.o
libs/acn/E131TestFramework.cpp
In file included from
/opt/ext-toolchain/arm-buildroot-linux-gnueabihf/include/c++/6.1.0/ext/string_conversions.h:41:0,
                 from
/opt/ext-toolchain/arm-buildroot-linux-gnueabihf/include/c++/6.1.0/bits/basic_string.h:5402,
                 from
/opt/ext-toolchain/arm-buildroot-linux-gnueabihf/include/c++/6.1.0/string:52,
                 from ./tools/ola_trigger/config.ypp:2:
/opt/ext-toolchain/arm-buildroot-linux-gnueabihf/include/c++/6.1.0/cstdlib:75:25:
fatal error: stdlib.h: No such file or directory
 #include_next <stdlib.h>
                         ^
compilation terminated.
```

The C++ library in GCC 6 now provides its own `<stdlib.h>` header that
wraps the C library header of the same name, so in `<cstdlib>` the
header include

```
#include <stdlib.h>
```

has become

```
#include_next <stdlib.h>
```

`#include_next` is sensitive to the order of directories in the
preprocessor's search path, so if that order is changed with `-isystem`
then the compiler can't find the right header:

```
[1] /usr/arm-buildroot-linux-gnueabihf/sysroot/usr/include
[2] /opt/ext-toolchain/arm-buildroot-linux-gnueabihf/include/c++/6.1.0
[..]
End of search list.
```

`<cstdlib>` is located in [2] whereas `<stdlib.h>` (C library header) is
in [1]. In this case, the `#include_next <stdlib.h>` statement in
`<cstdlib>`, located in [2], is evaluated **after** the search path [1],
so the compiler does not find the right system header.

The problem is that the OLA build system replaces the `-I` in the CFLAGS
from libprotobuf with `-isystem` to fix some warnings treated as errors
in the libprotobuf header files.

`-isystem` should be used to suppress warnings in system headers only
and the libprotobuf header files are not system files.

The correct fix is to compile with less restrictions and remove
`-Werror` for the build.

As using `-isystem` is reordering GCCs search path and using `-isystem`
is really not necessary, remove the faulty replacement of `-I`.

Upstream status: https://github.com/OpenLightingProject/ola/pull/1126

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
---
 config/ola.m4 | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/config/ola.m4 b/config/ola.m4
index 2796cfb..d3b8cc8 100644
--- a/config/ola.m4
+++ b/config/ola.m4
@@ -24,9 +24,6 @@ AC_DEFUN([PROTOBUF_SUPPORT],
 AC_REQUIRE_CPP()
 PKG_CHECK_MODULES(libprotobuf, [protobuf >= $1])
 
-# We want to replace -I with -isystem here to disable errors in the .h files
-# See https://groups.google.com/forum/#!topic/open-lighting/39Mj0KXlCIk
-libprotobuf_CFLAGS=`echo $libprotobuf_CFLAGS | sed 's/-I/-isystem /'`
 AC_SUBST([libprotobuf_CFLAGS])
 
 AC_ARG_WITH([protoc],
-- 
2.10.0