Remove replacing -I with -isystem

[joerg-krause]

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.

Closes: #1125

[nomis52]

Seems legit.

[peternewman]

Hi @joerg-krause thanks for this.

Firstly can you resync, as we've just merged some more changes into master. Better yet, please can you target our 0.10 branch, so we can get this into 0.10.3 if it's affecting current builds.

You'll also need to get Travis to pass, ignore the lint fails, as that is already fixed in 0.10 (and the will appear in master soon). You need to get the two Mac builds to compile at least (there's currently an issue with one of the Mac checks that I still need to fix).

They're currently failing with:
'''
/usr/local/bin/protoc --cpp_out common/protocol --proto_path ../../common/protocol ../../common/protocol/Ola.proto
[libprotobuf WARNING google/protobuf/compiler/parser.cc:546] No syntax specified for the proto file: Ola.proto. Please use 'syntax = "proto2";' or 'syntax = "proto3";' to specify a syntax version. (Defaulted to proto2 syntax.)
depbase=echo protoc/CppFileGenerator.o | sed 's|[^/]*$|.deps/&|;s|\.o$||';
g++ -DHAVE_CONFIG_H -I. -I../.. -I../../include -I./include -Wall -Wformat -W -fvisibility-inlines-hidden -D_THREAD_SAFE -I/usr/local/Cellar/protobuf/3.1.0/include -Werror -g -O2 -std=gnu++98 -D_THREAD_SAFE -MT protoc/CppFileGenerator.o -MD -MP -MF $depbase.Tpo -c -o protoc/CppFileGenerator.o ../../protoc/CppFileGenerator.cpp &&
mv -f $depbase.Tpo $depbase.Po
In file included from ../../protoc/CppFileGenerator.cpp:37:
In file included from /usr/local/Cellar/protobuf/3.1.0/include/google/protobuf/descriptor.h:59:
/usr/local/Cellar/protobuf/3.1.0/include/google/protobuf/stubs/shared_ptr.h:441:58: error: unused parameter 'other' [-Werror,-Wunused-parameter]
enable_shared_from_this(const enable_shared_from_this& other) { }
^
/usr/local/Cellar/protobuf/3.1.0/include/google/protobuf/stubs/shared_ptr.h:442:69: error: unused parameter 'other' [-Werror,-Wunused-parameter]
enable_shared_from_this& operator=(const enable_shared_from_this& other) {
^
'''

We worked around some similar issues here so you can fix it in a similar way:
https://github.com/OpenLightingProject/ola/pull/1111/files

[joerg-krause]

I opened a new PR #1130 which targets the 0.10.2 branch.

[peternewman]

Replaced by #1130.