GCC 4.5 compatibility: constexpr-related issues.

src/Magnum/MultisampleTexture.h

@@ -40,9 +40,10 @@ namespace Magnum {
 
 namespace Implementation {
     template<UnsignedInt> constexpr GLenum multisampleTextureTarget();
-    template<> constexpr GLenum multisampleTextureTarget<2>() { return GL_TEXTURE_2D_MULTISAMPLE; }
+    /* GCC 4.5 doesn't have constexpr, so it needs inline */
+    template<> constexpr inline GLenum multisampleTextureTarget<2>() { return GL_TEXTURE_2D_MULTISAMPLE; }
     #ifndef MAGNUM_TARGET_GLES
-    template<> constexpr GLenum multisampleTextureTarget<3>() { return GL_TEXTURE_2D_MULTISAMPLE_ARRAY; }
+    template<> constexpr inline GLenum multisampleTextureTarget<3>() { return GL_TEXTURE_2D_MULTISAMPLE_ARRAY; }
     #endif
 
     template<UnsignedInt dimensions> typename DimensionTraits<dimensions, Int>::VectorType maxMultisampleTextureSize();

src/Magnum/Texture.h

@@ -40,11 +40,12 @@ namespace Magnum {
 
 namespace Implementation {
     template<UnsignedInt> constexpr GLenum textureTarget();
+    /* GCC 4.5 doesn't have constexpr, so it needs inline */
     #ifndef MAGNUM_TARGET_GLES
-    template<> constexpr GLenum textureTarget<1>() { return GL_TEXTURE_1D; }
+    template<> constexpr inline GLenum textureTarget<1>() { return GL_TEXTURE_1D; }
     #endif
-    template<> constexpr GLenum textureTarget<2>() { return GL_TEXTURE_2D; }
+    template<> constexpr inline GLenum textureTarget<2>() { return GL_TEXTURE_2D; }
-    template<> constexpr GLenum textureTarget<3>() {
+    template<> constexpr inline GLenum textureTarget<3>() {
         #ifndef MAGNUM_TARGET_GLES2
         return GL_TEXTURE_3D;
         #else

src/Magnum/TextureArray.h

@@ -41,10 +41,11 @@ namespace Magnum {
 
 namespace Implementation {
     template<UnsignedInt> constexpr GLenum textureArrayTarget();
+    /* GCC 4.5 doesn't have constexpr, so it needs inline */
     #ifndef MAGNUM_TARGET_GLES
-    template<> constexpr GLenum textureArrayTarget<1>() { return GL_TEXTURE_1D_ARRAY; }
+    template<> constexpr inline GLenum textureArrayTarget<1>() { return GL_TEXTURE_1D_ARRAY; }
     #endif
-    template<> constexpr GLenum textureArrayTarget<2>() { return GL_TEXTURE_2D_ARRAY; }
+    template<> constexpr inline GLenum textureArrayTarget<2>() { return GL_TEXTURE_2D_ARRAY; }
 }
 
 /**