RULE-6-1: Permit bitfields of other integer types, depending on the compiler

[lcartey]

Affected rules

• RULE-6-1

Description

Support for the use of bitfields on integer types outside of unsigned int and signed int depends on the implementation.

• gcc - permits any integer type to be use for bitfields, per https://gcc.gnu.org/onlinedocs/gcc/Structures-unions-enumerations-and-bit-fields-implementation.html.
• armclang - "Enumeration types, long and long long (signed and unsigned) are allowed as bitfield types." https://developer.arm.com/documentation/100067/0612/Standard-C-Implementation-Definition/Structures--unions--enumerations--and-bitfields
• clang - I believe it supports at least long and long long, but I cannot find canonical documentation for that. It is alluded to elsewhere, though, e.g. https://www.open-std.org/jtc1/sc22/wg14/www/docs/n2774.htm.
• qcc - no information, would need some research

[rvermeulen]

Based on https://godbolt.org/z/Yfha6Gfhd we can assume compatibility between Gcc and Clang for the versions we support.