Clean up the cstest documentation and build instructions.

[Rot127]

Your checklist for this pull request

• I've documented or updated the documentation of every API function and struct this PR changes.
• I've added tests that prove my fix is effective or that my feature works (if possible)

Detailed description

There happened some confusion because the docs were not up to date.

Test plan

...

Closing issues

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[hainest]

DOWNLOAD_EXTRACT_TIMESTAMP wasn't added until 3.24. Would it be possible for Capstone to use this conditionally? Something like

if(CMAKE_VERSION VERSION_GREATER_EQUAL "3.24.0")
  set(DOWNLOAD_EXTRACT_TIMESTAMP "DOWNLOAD_EXTRACT_TIMESTAMP true")
endif()

ExternalProject_Add(cmocka_ext
    PREFIX extern
    URL "https://cmocka.org/files/1.1/cmocka-1.1.7.tar.xz"
    URL_HASH SHA256=810570eb0b8d64804331f82b29ff47c790ce9cd6b163e98d47a4807047ecad82
    ${DOWNLOAD_EXTRACT_TIMESTAMP}
    CONFIGURE_COMMAND cmake -DBUILD_SHARED_LIBS=OFF -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE} ../cmocka_ext/
    BUILD_COMMAND cmake --build . --config Release
    BUILD_BYPRODUCTS "${CMOCKA_LIB_FILE}"
    INSTALL_COMMAND ""
)

and the same for libcyaml_ext.

[Rot127]

In general yes. IIRC there was also another reason why cmake >=3.24 was needed. But I forgot why and if at all.
Would you mind to open a PR please?