cmake: Fix toolchain including unsupported languages

[amyspark]

The most egregious cases are Nasm (which needs to be transformed to ASM_NASM) and Rust (which is not yet supported by CMake).

Without this change, projects including multiple languages will generate a toolchain file e.g.

set(CMAKE_SIZEOF_VOID_P "8")
set(CMAKE_C_COMPILER "C:/Program Files (x86)/Microsoft Visual Studio/2022/BuildTools/VC/Tools/MSVC/14.44.35207/bin/HostX64/x64/cl.EXE")
set(CMAKE_CXX_COMPILER "C:/Program Files (x86)/Microsoft Visual Studio/2022/BuildTools/VC/Tools/MSVC/14.44.35207/bin/HostX64/x64/cl.EXE")
set(CMAKE_RUST_COMPILER "C:/Users/Amalia/.cargo/bin/rustc.EXE" "-C" "linker=link")
set(CMAKE_NASM_COMPILER "C:/Users/Amalia/.cargo/bin/nasm.EXE")

which will then cause:

WARNING: CMake Toolchain: Failed to determine CMake compilers state
 -- return code: 1
 -- stdout: Put cmake in trace mode, but with variables expanded.
 -- stdout: Put cmake in trace mode and sets the trace output format.
 -- stdout: Not searching for unused variables given on the command line.
 -- stdout: Put cmake in trace mode and redirect trace output to a file instead of stderr.
 -- stdout: Trace will be written to cmake_trace.txt
 -- stdout: -- Configuring incomplete, errors occurred!
 -- stdout: 
 -- stderr: CMake Error: Could not find cmake module file: CMakeDetermineRUSTCompiler.cmake
 -- stderr: CMake Error: Error required internal CMake variable not set, cmake may not be built correctly.
 -- stderr: Missing variable is:
 -- stderr: CMAKE_RUST_COMPILER_ENV_VAR
 -- stderr: CMake Error: Could not find cmake module file: E:/gstreamer/build/meson-private/__CMake_compiler_info__/CMakeFiles/3.27.9/CMakeRUSTCompiler.cmake
 -- stderr: CMake Error at CMakeLists.txt:3 (project):
 -- stderr:   The CMAKE_RUST_COMPILER:
 -- stderr: 
 -- stderr:     C:/Users/Amalia/.cargo/bin/rustc.EXE;-C;linker=link
 -- stderr: 
 -- stderr:   is not a full path to an existing compiler tool.
 -- stderr: 
 -- stderr:   Tell CMake where to find the compiler by setting the CMake cache entry
 -- stderr:   CMAKE_RUST_COMPILER to the full path to the compiler, or to the compiler
 -- stderr:   name if it is in the PATH.
 -- stderr: 
 -- stderr: 
 -- stderr: CMake Error: Could not find cmake module file: CMakeRUSTInformation.cmake
 -- stderr: 

See https://cmake.org/cmake/help/v4.0/command/project.html

[nirbheek]

LGTM, will merge in 24h

[dcbaker]

I went ahead and merged this (since it has my review and nirbheek's). I also added it to the 1.8.1 milestone, since it's a bug fix and minimally invasive.