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5c5b4df6d3
GCC 11+ requires compiler being used to support C++11 standard [1].
And while GCC starting from 6.x has C++11 support enabled by default [2],
older versions need to be forced to implement it with "-std=gnu++11" and luckily
GCC's build-system takes care of that:
1. For ${host} compiler - [1]
2. For ${build} compiler - [3, 4]
In a nutshell the configure script tries a couple of options and the one which
helps to build a test source gets appended to CXX (not CXXFLAGS!),
so on say CentOS 7.x with GCC 4.8.5 during cross-compilation of GCC
CXX="x86_64-build_pc-linux-gnu-g++ -std=gnu++11". And all is good.
But in case of canadian cross due to [5] we for some reason* force set
CXX_FOR_BUILD with just a compiler name, effectively overriding all the
magic done by GCC's internals described above.
This leads to a compilation failures like that:
------------------------------------->8----------------------------------
[ALL ] In file included from /usr/include/c++/4.8.2/type_traits:35:0,
[ALL ] from .../HOST-x86_64-apple-darwin14/arc-gcc11-elf/src/gcc/gcc/system.h:244,
[ALL ] from .../HOST-x86_64-apple-darwin14/arc-gcc11-elf/src/gcc/gcc/gengtype.c:26:
[ERROR] /usr/include/c++/4.8.2/bits/c++0x_warning.h:32:2: error: #error This file requires compiler and library support for the ISO C++ 2011 standard. This support is currently experimental, and must be enabled with the -std=c++11 or -std=gnu++11 compiler options.
[ALL ] #error This file requires compiler and library support for the ^
------------------------------------->8----------------------------------
* my guess that [5] was done because back in the day indeed we used to have
"--build=${CT_BUILD} --host=${CT_HOST}" in do_cc_core(). But now after [6]
this is no longer necessary as we use "--build=${CT_BUILD} --host=${CT_BUILD}"
and all is safe and clean. So yet another old quirk goes away - hooray!
[1] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=5329b59a2e13dabbe2038af0fe2e3cf5fc7f98ed
[2] https://gcc.gnu.org/gcc-6/changes.html
[3] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96612
[4] https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=7ffcf5d61174dda1f39a623e15f7e5d6b98bbafc
[5] 9c6c090d7b
[6] 08161250ed
Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>