Compilation error building QT 5.5.1 on Gentoo Linux

[A Former User]

GCC version 4.9.3
glibc 2.21-r1

ERROR
qmimetype.o fails

/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/ext/concurrence.h:122:34: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘short int’ in initialization
__gthread_mutex_t _M_mutex = __GTHREAD_MUTEX_INIT;

/usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/include/g++-v4/ext/concurrence.h:177:44: error: cannot convert ‘<brace-enclosed initializer list>’ to ‘short int’ in initialization
__gthread_recursive_mutex_t _M_mutex = __GTHREAD_RECURSIVE_MUTEX_INIT;

My build.log.
The concurrence header file I have on my system.

How do i resolve this?