Error with long doubles on PowerPC when compiling with gcc

I'm running into a curious bug when I assign values to long double variable types. (PowerPC architecture, gcc v4.9.2)

Specifically:

const constexpr long double DEGREE_TO_RAD = 0.0174532925199432954743716805978693;
const constexpr long double RAD_TO_DEGREE = 1. / DEGREE_TO_RAD;

seems to result in the following compiler error:

error: ‘(1.0e+0l / 1.74532925199432954743716805978693e-2l)’ is not a constant expression
 const constexpr long double RAD_TO_DEGREE = 1. / DEGREE_TO_RAD;

I am not an expert in C++; this is software I'm attempting to build specifically for my development machine's environment. However, my research has led me to the following tidbit:

On some PowerPC and SPARCv9 machines, long double is implemented as a double-double arithmetic, where a long double value is regarded as the exact sum of two double-precision values, giving at least a 106-bit precision; with such a format, the long double type does not conform to the IEEE floating-point standard. Otherwise, long double is simply a synonym for double (double precision). [wiki]

Which leads me to believe the build failure is due to long double having a different interpretation in my architecture vs the standard x86. Changing long double to double in the source allows the compilation to succeed. Is this a coincidence? Why would g++ throw a fit about it in this instance?