I don't think I ever write C code that I intent to only be compiled using one compiler. One of the primary reasons I use C is to write cross-platform code, so I care about GCC, Clang, and VS, at least.
GCC and Clang are both cross-platform, and users typically don’t care about which compiler you used to produce the binary. At least until the early 2010s plenty of projects used GCC-specific features and wouldn’t compile with Clang. The situation must be better now but I bet GCC is still the only blessed compiler for many maintenance-only code bases.
