Earlier quoted context omitted.
Even worse, the C parts of the Go runtime are being rewritten in Go. The Plan 9 C compiler is going away along with all the other C bits as the compilers themselves are being translated to Go. In short, this will go away very soon. Possibly even Go 1.4. Definitely Go 1.5.
The way he describes linking/including .c files is identical to how you can link-in/include assembly code via .s files. I don't see the latter going away (the standard `math` package uses this extensively), so why should the former---even if Go 1.4 or later itself doesn't use it..
The main Go distribution will always have assembly source files: there are always going to be special instructions or routines, such as low-level startup, that must be written at that level. The same is not true of (non-gcc) C source files.
Once the main Go distribution has no non-gcc C source files, we _will_ delete the Plan 9 C compilers. There is no reason to maintain them if we are not using them.