Enable Buffer::{map,unmap}Sub() for Doxygen.

Otherwise the existence of these function will not be known at all.

src/Magnum/Buffer.cpp

@@ -343,7 +343,7 @@ void* Buffer::map(const MapAccess access) {
     return (this->*Context::current()->state().buffer->mapImplementation)(access);
 }
 
-#ifdef CORRADE_TARGET_NACL
+#if defined(DOXYGEN_GENERATING_OUTPUT) || defined(CORRADE_TARGET_NACL)
 void* Buffer::mapSub(const GLintptr offset, const GLsizeiptr length, const MapAccess access) {
     CORRADE_ASSERT(!_mappedBuffer, "Buffer::mapSub(): the buffer is already mapped", nullptr);
     return _mappedBuffer = glMapBufferSubDataCHROMIUM(GLenum(bindSomewhereInternal(_targetHint)), offset, length, GLenum(access));
@@ -361,7 +361,7 @@ Buffer& Buffer::flushMappedRange(const GLintptr offset, const GLsizeiptr length)
 
 bool Buffer::unmap() { return (this->*Context::current()->state().buffer->unmapImplementation)(); }
 
-#ifdef CORRADE_TARGET_NACL
+#if defined(DOXYGEN_GENERATING_OUTPUT) || defined(CORRADE_TARGET_NACL)
 void Buffer::unmapSub() {
     CORRADE_ASSERT(_mappedBuffer, "Buffer::unmapSub(): the buffer is not mapped", );
     glUnmapBufferSubDataCHROMIUM(_mappedBuffer);

src/Magnum/Buffer.h

@@ -1178,7 +1178,7 @@ class MAGNUM_EXPORT Buffer: public AbstractObject {
             return static_cast<T*>(map(access));
         }
 
-        #ifdef CORRADE_TARGET_NACL
+        #if defined(DOXYGEN_GENERATING_OUTPUT) || defined(CORRADE_TARGET_NACL)
         /**
          * @brief Map portion of buffer to client memory
          * @param offset    Offset into the buffer
@@ -1279,7 +1279,7 @@ class MAGNUM_EXPORT Buffer: public AbstractObject {
          */
         bool unmap();
 
-        #ifdef CORRADE_TARGET_NACL
+        #if defined(DOXYGEN_GENERATING_OUTPUT) || defined(CORRADE_TARGET_NACL)
         /**
          * @brief Unmap portion of buffer
          *