MFC r309191 (by rakuco):

fdt: Expect strchr() to return a const char*

In C, strchr(3) returns a char*, whereas C++ defines two overloads:

• const char *strchr(const char*, int)
• char *strchr(char*, int)

Building fdt.cc (with the WITHOUT_GPL_DTC knob set) with libc++ 3.9.0 (imported
in r309124) was failing because libc++ r260377 added the first overload to
string.h, leading to failures such as:

fdt.cc:1638:8: error: cannot initialize a variable of type 'char *' with an
rvalue of type 'const char *'

Just define val as a const char* to fix it.

Upstreamed in https://github.com/davidchisnall/dtc/pull/14