gcc 14.1+ and clang 15+ with gcc/clang no-implicit-function-declaration isn't enforced as an error

[sean-mcmanus]

While it's not valid in the C99 standard, it looks like all the C compilers we support don't support this rule, I assume because it would be a breaking change with C89.

In GCC, implicit function declaration is an error even without any additional warning flags. This is with --std=c23; I'm not sure about C89. You have to explicitly turn this off with -Wno-implicit-function-declaration.

Originally posted by @cD1rtX3 in #828

[cD1rtX3]

I don't think this is specific to C23; it's just the version of the standard that I use.

[sean-mcmanus]

@sean-mcmanus You are right -- it appears the warning is promoted to an error by default starting with gcc 14.1 and clang 15 even with c17 -- it seems like our EDG compiler should be outputting an error when those compiler versions are detected.