Fix compilation errors on modern C compilers and CMake >= 3.28

[ludomal]

This PR fixes compilation errors that prevent the STL from building with modern C compilers (Clang 17+, GCC 14+) and CMake >= 3.28.

Changes

CMake version policy (CMakeLists.txt, src/wmc_tool/CMakeLists.txt)

CMake 3.28+ removed compatibility with cmake_minimum_required(VERSION) values below 3.5. The previous VERSION 3.1 caused a fatal configuration error:

Compatibility with CMake < 3.5 has been removed from CMake.

Updated to use the range syntax VERSION 3.10...3.31:

• The minimum (3.10) ensures broad compatibility with systems still running older CMake (e.g., Ubuntu 20.04 ships 3.16).
• The maximum (3.31) tells CMake which policy version the project has been tested against, preventing unexpected policy changes from newer CMake versions.
• This is the CMake-recommended approach for projects that need to support a range of CMake versions.

src/g711/shiftbit.c - incompatible pointer to integer conversion

fread() was called with fi (an int file descriptor from fileno()) instead of Fi (the FILE * from fopen()). This was introduced when migrating from POSIX read() to fread() but the argument was not updated.

src/mnru/mnru.c - incompatible integer to pointer conversion

s->seed is declared as long but was assigned NULL (a pointer type). Changed to 0.

src/unsup/endian.c - implicit int return type

reverse_endian_short() and reverse_endian_long() had no return type specifier, which defaults to int (invalid in C99 and later). Added explicit void return types. Also fixed signedness mismatch in test_s()/test_l() local variables.

Testing

Successfully compiled and linked (100% targets) on:

• macOS 26 (arm64) with Apple Clang 17, CMake 4.0.2
• Ubuntu 24 (x86_64) with GCC/Clang, CMake 3.28.3

No functional changes (only type corrections and CMake version policy update).