How to compile C code that #includes C++ code?

I have to compile generated C code that #includes C++ headers and it get it to work on Linux, OS X and Windows. I put the #includes myself to be able to interact with C++ code from it.

The C code however is such that a strict compiler would catch errors that could be treated as warnings. I want to pass these off as warnings as most of this is generated code which I don't have control over.

Here are my attempts to compile it (I use CMake, btw):

(I use these flags: -Wno-write-strings -Wno-error -fpermissive)

• Treat the entire project as C++ code: works on Linux (with g++) but on OS X I get:

With Clang:

error: assigning to 'char *' from incompatible type 'const char *'

With g++:

/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:18:no such instruction: `vmovdqa LC0(%rip), %xmm3'
/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:19:no such instruction: `vmovdqa LC1(%rip), %xmm2'
/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:20:no such instruction: `vmovdqu (%rsi), %xmm7'
/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:21:no such instruction: `vmovdqu 16(%rsi), %xmm8'
/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:22:no such instruction: `vmovdqa LC2(%rip), %xmm1'
/var/folders/hf/5dbkbqrx5p3bmnpdqqy4wgpr0000gn/T//ccvMHo2S.s:23:no such instruction: `vpshufb %xmm3, %xmm7,%xmm6'

• Treat C code as C code:

Doesn't find <atomic>

 fatal error: atomic: No such file or directory
 #include <atomic>

• Use -Wa -q flags as per this answer: http://ift.tt/1BRtFBu

Flag becomes invalid.

clang: error: unknown argument: '-q'
clang: warning: treating 'c' input as 'c++' when in C++ mode, this behavior is deprecated

How do I go about building this?