Shaders: prefix GLSL workaround macros with MAGNUM_.

In order to prepare them for being included for all shader code, not
just own builtin shaders.

src/Magnum/DebugTools/TextureImage.vert

@@ -23,12 +23,12 @@
     DEALINGS IN THE SOFTWARE.
 */
 
-#ifdef DISABLE_GL_MAGNUM_shader_vertex_id
+#ifdef MAGNUM_DISABLE_GL_MAGNUM_shader_vertex_id
 in lowp vec4 position;
 #endif
 
 void main() {
-    #ifndef DISABLE_GL_MAGNUM_shader_vertex_id
+    #ifndef MAGNUM_DISABLE_GL_MAGNUM_shader_vertex_id
     gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
                        (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
     #else

src/Magnum/Shaders/FullScreenTriangle.glsl

@@ -25,7 +25,7 @@
 
 /* Inputs */
 
-#if !defined(NEW_GLSL) || defined(DISABLE_GL_MAGNUM_shader_vertex_id)
+#if !defined(NEW_GLSL) || defined(MAGNUM_DISABLE_GL_MAGNUM_shader_vertex_id)
 #ifndef NEW_GLSL
 #define in attribute
 #endif
@@ -33,7 +33,7 @@ in lowp vec4 position;
 #endif
 
 void fullScreenTriangle() {
-    #if defined(NEW_GLSL) && !defined(DISABLE_GL_MAGNUM_shader_vertex_id)
+    #if defined(NEW_GLSL) && !defined(MAGNUM_DISABLE_GL_MAGNUM_shader_vertex_id)
     gl_Position = vec4((gl_VertexID == 2) ?  3.0 : -1.0,
                        (gl_VertexID == 1) ? -3.0 :  1.0, 0.0, 1.0);
     #else

src/Magnum/Shaders/Implementation/CreateCompatibilityShader.h

@@ -49,16 +49,16 @@ inline GL::Shader createCompatibilityShader(const Utility::Resource& rs, GL::Ver
 
     #ifndef MAGNUM_TARGET_GLES
     if(GL::Context::current().isExtensionDisabled<GL::Extensions::ARB::explicit_attrib_location>(version))
-        shader.addSource("#define DISABLE_GL_ARB_explicit_attrib_location\n"_s);
+        shader.addSource("#define MAGNUM_DISABLE_GL_ARB_explicit_attrib_location\n"_s);
     if(GL::Context::current().isExtensionDisabled<GL::Extensions::ARB::shading_language_420pack>(version))
-        shader.addSource("#define DISABLE_GL_ARB_shading_language_420pack\n"_s);
+        shader.addSource("#define MAGNUM_DISABLE_GL_ARB_shading_language_420pack\n"_s);
     if(GL::Context::current().isExtensionDisabled<GL::Extensions::ARB::explicit_uniform_location>(version))
-        shader.addSource("#define DISABLE_GL_ARB_explicit_uniform_location\n"_s);
+        shader.addSource("#define MAGNUM_DISABLE_GL_ARB_explicit_uniform_location\n"_s);
     #endif
 
     #ifndef MAGNUM_TARGET_GLES2
     if(type == GL::Shader::Type::Vertex && GL::Context::current().isExtensionDisabled<GL::Extensions::MAGNUM::shader_vertex_id>(version))
-        shader.addSource("#define DISABLE_GL_MAGNUM_shader_vertex_id\n"_s);
+        shader.addSource("#define MAGNUM_DISABLE_GL_MAGNUM_shader_vertex_id\n"_s);
     #endif
 
     shader.addSource(rs.getString("compatibility.glsl"_s));

src/Magnum/Shaders/compatibility.glsl

@@ -27,18 +27,18 @@
     #define NEW_GLSL
 #endif
 
-#if !defined(GL_ES) && defined(GL_ARB_explicit_attrib_location) && !defined(DISABLE_GL_ARB_explicit_attrib_location)
+#if !defined(GL_ES) && defined(GL_ARB_explicit_attrib_location) && !defined(MAGNUM_DISABLE_GL_ARB_explicit_attrib_location)
     #extension GL_ARB_explicit_attrib_location: enable
     #define EXPLICIT_ATTRIB_LOCATION
 #endif
 
-#if !defined(GL_ES) && defined(GL_ARB_shading_language_420pack) && !defined(DISABLE_GL_ARB_shading_language_420pack)
+#if !defined(GL_ES) && defined(GL_ARB_shading_language_420pack) && !defined(MAGNUM_DISABLE_GL_ARB_shading_language_420pack)
     #extension GL_ARB_shading_language_420pack: enable
     #define RUNTIME_CONST
     #define EXPLICIT_BINDING
 #endif
 
-#if !defined(GL_ES) && defined(GL_ARB_explicit_uniform_location) && !defined(DISABLE_GL_ARB_explicit_uniform_location)
+#if !defined(GL_ES) && defined(GL_ARB_explicit_uniform_location) && !defined(MAGNUM_DISABLE_GL_ARB_explicit_uniform_location)
     #extension GL_ARB_explicit_uniform_location: enable
     #define EXPLICIT_UNIFORM_LOCATION
 #endif