Include path using clang++ and SDL - c++

Question

I have an SDL program that I need to compile on my Mac with the line:
#include <SDL.h>
I have libsdl installed using MacPorts, and the output of sdl-config --cflags is:
-I/opt/local/include/SDL -D_GNU_SOURCE=1 -D_THREAD_SAFE
which is, indeed, where the SDL headers are located:
$ ls /opt/local/include/SDL
SDL.h SDL_cpuinfo.h SDL_keyboard.h SDL_rwops.h
...
and then my Makefile invokes the compiler (clang++) with:
CXXFLAGS=`sdl-config --cflags`
Invoking the compiler with -v shows that it is being included in the search path:
#include "..." search starts here:
#include <...> search starts here:
/opt/local/include/SDL
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1
/usr/local/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/clang/6.1.0/include
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/include
/usr/include
/System/Library/Frameworks (framework directory)
/Library/Frameworks (framework directory)
End of search list.
but the compiler errors with:
./drawable.h:4:10: fatal error: 'SDL.h' file not found
#include <SDL.h>
^
It compiles fine if I change it to #include <SDL/SDL.h>, but other (Linux) machines that the program needs to compile on don't specify it that way. What am I not understanding about how to set up my include path?
EDIT:
Here's a minimal example:
$ cat main.cpp
#include <SDL.h>
int main(int argc, char *argv[]) { }
$ sdl-config --cflags
-I/opt/local/include/SDL -D_GNU_SOURCE=1 -D_THREAD_SAFE
$ ls /opt/local/include/SDL/SDL.h
/opt/local/include/SDL/SDL.h
$ clang++ -v `sdl-config --cflags` main.cpp
...
#include "..." search starts here:
#include <...> search starts here:
/opt/local/include/SDL
....
main.cpp:1:10: fatal error: 'SDL.h' file not found
#include <SDL.h>
^
1 error generated.
ANSWER:
SDL.h turned out to be a broken symbolic link, my own fault.

Answer 1

I think in your Makefile, CXXFLAGS are not included in the compilation command.
Your Makefile should have something like:
$(CXX) $(CXXFLAGS) $(SRC) -o $(EXE)

Answer 2

OK, this just turned out to be my own stupidity, but maybe someone else will benefit from it. I created the /opt/local/include/SDL directory and filled it with soft links to the actual header files in /Library/Frameworks/SDL.framework/Headers, because my project relied on the former. I then, in working on another means of installing SDL, deleted the framework, leaving a bunch of dead links. ls without arguments helpfully showed me filenames, but not that they were links, which I had forgotten by this point. So, SDL.h didn't really exist. A smarter approach might have been to soft link the directory, which would have probably given a more helpful error message, but I was trying to put some other SDL package links in there too.