fix: declarations

[gottfriedleibniz]

Inspecting the symbols of a library using glm (compiled w/ default visibility) lead me to notice these being externalized:

unsigned int glm::findEigenvaluesSymReal<2, float, (glm::qualifier)3>(glm::mat<2, 2, float, (glm::qualifier)3> const&, glm::vec<2, float, (glm::qualifier)3>&, glm::mat<2, 2, float, (glm::qualifier)3>&)
unsigned int glm::findEigenvaluesSymReal<3, float, (glm::qualifier)3>(glm::mat<3, 3, float, (glm::qualifier)3> const&, glm::vec<3, float, (glm::qualifier)3>&, glm::mat<3, 3, float, (glm::qualifier)3>&)
unsigned int glm::findEigenvaluesSymReal<4, float, (glm::qualifier)3>(glm::mat<4, 4, float, (glm::qualifier)3> const&, glm::vec<4, float, (glm::qualifier)3>&, glm::mat<4, 4, float, (glm::qualifier)3>&)
glm::mat<2, 2, float, (glm::qualifier)3> glm::computeCovarianceMatrix<2, float, (glm::qualifier)3, ...
glm::mat<2, 2, float, (glm::qualifier)3> glm::computeCovarianceMatrix<2, float, (glm::qualifier)3, ...
glm::mat<3, 3, float, (glm::qualifier)3> glm::computeCovarianceMatrix<3, float, (glm::qualifier)3, ...
glm::qua<float, (glm::qualifier)0> glm::toQuat<float, (glm::qualifier)0>(glm::mat<4, 4, float, (glm::qualifier)0> const&)
glm::qua<float, (glm::qualifier)3> glm::toQuat<float, (glm::qualifier)3>(glm::mat<3, 3, float, (glm::qualifier)3> const&)

This commit fixes the declarations to the listed functions.

[christophe-lunarg]

Thanks for contributing!