Add AC_OBSOLETE to m4/ax_have_opengl.m4
Use AX_COMPILER_VENDOR for AX_CXX_COMPILER_VENDOR
Modernize ax_cxx_bool.m4

Use modern autoconf construct like AS_IF
Modernize AX_CXX_COMPLEX_MATH_IN_NAMESPACE_STD
Modernize  m4/ax_cxx_const_cast.m4
Modernize ax_cxx_templates.m4
Modernize ax_cxx_default_template_parameters.m4