Automotive embedded C developer here. Most of the code in this industry is implemented in a subset of ANSI C90. The reason is not header files, libraries or linker scripts. The reason is as the grandparent post points out: compiler availability.
For rare targets, there's just no money in making a compiler work for more than this small subset of C. My favorite example is the compiler for a really strange architecture where everything is 24 bits. Char is short is long is a pointer.
Bigger controllers tend to be ARM-based, so it's getting better.
Also Tricore has a big share, but their compiler support is getting better. There was even a rust compiler being announced recently, though I doubt it's using LLVM backend, so it's likely to be behind in terms of features.
For rare targets, there's just no money in making a compiler work for more than this small subset of C. My favorite example is the compiler for a really strange architecture where everything is 24 bits. Char is short is long is a pointer.
Bigger controllers tend to be ARM-based, so it's getting better.
Also Tricore has a big share, but their compiler support is getting better. There was even a rust compiler being announced recently, though I doubt it's using LLVM backend, so it's likely to be behind in terms of features.