build: silence GCC -Wpsabi notes on 32-bit ARM NIF builds

[cocoa-xu]

What

On 32-bit ARM (armv7l, armv6), GCC emits -Wpsabi notes when compiling the std::vector<int64_t> get_list/get_tuple helpers in the NIF:

note: parameter passing for argument of type std::vector<long long int>::iterator ... changed in GCC 7.1

These report the historic AAPCS ABI change introduced in GCC 7.1. They are harmless as long as the whole NIF is compiled with a single toolchain (always the case), but GCC writes them to stderr, so the Actions UI paints the otherwise-green precompile jobs with red Error: annotations.

Fix

Add -Wno-psabi to the evision target's warning flags, scoped to 32-bit ARM only:

if(CMAKE_SYSTEM_PROCESSOR MATCHES "arm" AND CMAKE_SIZEOF_VOID_P EQUAL 4)
    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wno-psabi")
endif()

MATCHES "arm" covers armv6/armv7l; the 4-byte-pointer clause excludes arm64; aarch64 never matches the string. Every other arch is untouched.

Validation

Reproduced against the exact CI compiler (arm-linux-gnueabihf-g++ 9.4, ubuntu:20.04):

• default -Wall -Wextra: 2 psabi notes per TU, exit 0 (never a hard error)
• with -Wno-psabi: 0 notes, exit 0
• armv7l cross-configure: predicate resolves TRUE, -Wno-psabi reaches the compile line, full rebuild yields 0 notes
• string match verified across the matrix: armv6/armv7l TRUE, aarch64 FALSE, arm64 excluded by the pointer-size clause

The flag is accepted as a no-op by GCC 13/15 and Apple clang 17, so newer-toolchain and macOS builds are unaffected.

Opening as draft.