package/cc-tool: fix gcc 5 issue

The version of boost.m4 initially included in cc-tool has an issue
with gcc5 (one of its tests fails due to the first change described in [1]
"Preprocessor issues").

This was fixed upstream (boost.m4 project) in Nov 2014 [2].

We add the latest commit [3] of upstream boost.m4 plus a patch from github PR
[4] to add detection for gcc 5.1.

Fixes:
http://autobuild.buildroot.net/results/a4c/a4c057e0b1ab6a2ffd69b27f6f5a79f98eb040f6/

[1]
https://gcc.gnu.org/gcc-5/porting_to.html

[2]
https://github.com/tsuna/boost.m4/commit/32553aaf4d5090da19aa0ec33b936982c685009f

[3]
https://github.com/tsuna/boost.m4/commit/d9ff75b6af66360d76f46f469a26ab18e24e1030

[4]
https://github.com/rubenk/boost.m4/commit/b879eb85f112cf054643d2e7f9544c230299c0b2



Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>