I've included the statically linked (CROSS) compiler,
GCC version 6.4.0, made from musl-cross-make.

By design, cross compilers won't look at the following
directories for libs/headers (they leave the host system's 
includes and headers directories alone)

/lib
/include
/usr/lib
/usr/include

So I've created a specs file using

gcc -dumpspecs > specs

and edited it and put it back in 

$(TOOLCHAIN)/lib/gcc/$(ARCH)-linux-musl/$(GCC_VERSION)/ 

so that it will look for the above directories on 
purpose and will save most people (including me) 
from linking nightmares.

I typically place the cross compiler at the top-most 
level of the unix file hierarchy for easy compiler access.

N.B: The supplied cross compiler already contains my
custom specs file.