Minimum supported version for C compiler

[franziskuskiefer]

Define GCC and clang minimum supported versions.

[beurdouche]

gcc 4.8 it is. Maybe someone has stronger requirements @polubelova @Frosne @protz ?

[msprotz]

There was a blog post somewhere where Mirage folks were unhappy with the __has_include (which we should now be able to get rid of). According to https://en.cppreference.com/w/cpp/compiler_support this is in GCC 5. So maybe they, too, we reliant on GCC 4.8...

[beurdouche]

I think @Frosne is running into exactly that right now in our CI.

[msprotz]

I'm happy to approve a PR that removes __has_include from lib/c/* and assumes everyone runs configure and thus has a valid config.h -- Mozilla has a hand-written config.h, correct?

[Frosne]

For now I solved it using these lines:

#if defined(__has_include)
#if __has_include("config.h")
#include "config.h"
#endif
#endif

If we don't want to remove config, it could be a way to go.

[msprotz]

Interesting. But then are you compiling AVX or AVX2 code? How are you defining HACL_CAN_COMPILE_VEC128?

[Frosne]

With these lines we have gcc-4.4 compiler also passes CI :)

[Frosne]

Interesting. But then are you compiling AVX or AVX2 code? How are you defining HACL_CAN_COMPILE_VEC128?

By adding -DHACL_CAN_COMPILE_VEC128/256 to CFLAGS

[msprotz]

Ok I thought about it and I believe your solution is actually even better. This means clients who want to integrate HACL have two options:

• -D... compiler options using their favorite build system to enable features depending on target support
• just running the configure script and leaving it up to us to set those flags in config.h -- this works for simple situations, but not all (e.g. cross-compiling on x64)

I'm happy to approve a PR to that effect. There are only a handful of places that use __has_include

[msprotz]

To be closed once I finish & merge #561