Fix processor detection in CMakeLists.txt

[jiegec]

CMAKE_SYSTEM_NAME is set to the OS name, e.g. Linux. It should check CMAKE_SYSTEM_PROCESSOR instead.

The regex is wrong: [i?86|x86] will matching anything containing 6, so it will take the wrong branch for many ISAs, e.g. riscv64 and even ARM64 when it is uppercased. It eventually leads to wrong DES encryption due to wrong sizeof(DES_LONG).

Handle cases when CMAKE_SYSTEM_PROCESSOR is upper-cased, e.g. in windows.

[jiegec]

CI failed in windows:

Building Custom Rule D:/a/portable/portable/crypto/CMakeLists.txt
  Assembling D:\a\portable\portable\crypto\aes\aes-masm-x86_64.S...
D:\a\portable\portable\crypto\aes\aes-masm-x86_64.S(1840): error A2189: invalid combination with segment alignment : 64 [D:\a\portable\portable\build\crypto\crypto_obj.vcxproj]
D:\a\portable\portable\crypto\aes\aes-masm-x86_64.S(2230): error A[21](https://github.com/libressl/portable/actions/runs/6068067965/job/16460548254?pr=909#step:6:22)89: invalid combination with segment alignment : 64 [D:\a\portable\portable\build\crypto\crypto_obj.vcxproj]
D:\a\portable\portable\crypto\aes\aes-masm-x86_64.S(2624): error A2189: invalid combination with segment alignment : 64 [D:\a\portable\portable\build\crypto\crypto_obj.vcxproj]

I don't have Windows environment to test.

[vszakats]

Another case is Universal macOS builds, setup with e.g.
CMAKE_OSX_ARCHITECTURES=arm64;x86_64.

I don't think the current build layout can handle that, and matching one
of the platforms seems wrong as well. Possibly ASM should be disabled
with multiple values there. I haven't made tests though.

It'd be useful to make that work out of the box. For that, the CPU
selection should probably be delegated to the C preprocessor by
#including the necessary ASM code into C at compile-time, while
keeping the set of source files the same, regardless of target CPU.

[busterb]

Hi, thanks for the PR. I think what you are doing here is correct; the Windows failure is due to it actually fixing the detection of processor and enabling MASM assembly in the build, which is coincidentally broken. I'll add a patch to this to work around that and fix the MASM in another patch set so this applies cleanly on its own.