[PATCH 0/2] cmake doc: modernize and cross-platform-ize the docs

Change the cmake docs to use one-command build instructions using options that "cmake" supports an ill our supported versions, and in 2/2 re-arrange the docs to make it clearer which part of the instructions are platform-specific.

Like the just-submitted [1] this extracted from [2], and the range diff below is to [2]. The only change since [2] is a trivial reflow change in the commit message.

There were no outstanding issues or feedback with this part of [2], so hopefully this can advance relatively quickly.

1. https://lore.kernel.org/git/patch-1.1-0fa41115261-20221219T102205Z-avarab@gmail.com/T/#u
2. https://lore.kernel.org/git/cover-v6-00.15-00000000000-20221206T001617Z-avarab@gmail.com/

Ævar Arnfjörð Bjarmason (2):
  cmake: use "-S" and "-B" to specify source and build directories
  cmake: update instructions for portable CMakeLists.txt

 contrib/buildsystems/CMakeLists.txt | 70 ++++++++++++++++++++---------
 1 file changed, 50 insertions(+), 20 deletions(-)

Range-diff:
 1:  fc190b379cd <  -:  ----------- cmake: don't invoke msgfmt with --statistics
 2:  1a11aa233a3 !  1:  2411acc9d4c cmake: use "-S" and "-B" to specify source and build directories
    @@ Commit message
         cmake: use "-S" and "-B" to specify source and build directories
     
         Rather than the multi-line "mkdir/cd/cmake" recipe provide an
    -    equivalent one-liner using the "-S" and "-B" options, and then suggest building with "make -C <build-dir>".
    +    equivalent one-liner using the "-S" and "-B" options, and then suggest
    +    building with "make -C <build-dir>".
     
         The rest of these instructions discuss e.g. running tests from our
         top-level "t/" directory, so it's more helpful to avoid changing the
 3:  b9ddb5db1d3 =  2:  d6058ed0f22 cmake: update instructions for portable CMakeLists.txt
 4:  7b7850c00ee <  -:  ----------- cmake: don't copy chainlint.pl to build directory
 5:  82ecb797915 <  -:  ----------- cmake: chmod +x the bin-wrappers/* & SCRIPT_{SH,PERL} & git-p4
 6:  1f326944a07 <  -:  ----------- cmake & test-lib.sh: add a $GIT_SOURCE_DIR variable
 7:  973c8038f54 <  -:  ----------- cmake: set "USE_LIBPCRE2" in "GIT-BUILD-OPTIONS" for test-lib.sh
 8:  b8448c7a8a6 <  -:  ----------- Makefile + test-lib.sh: don't prefer cmake-built to make-built git
 9:  5135e40969e <  -:  ----------- test-lib.sh: support a "GIT_TEST_BUILD_DIR"
10:  65204463730 <  -:  ----------- cmake: optionally be able to run tests before "ctest"
11:  e25992b16f1 <  -:  ----------- cmake: support GIT_TEST_OPTS, abstract away WIN32 defaults
12:  4905ce5321d <  -:  ----------- cmake: increase test timeout on Windows only
13:  6c6b530965d <  -:  ----------- cmake: only look for "sh" in "C:/Program Files" on Windows
14:  563f1b9b045 <  -:  ----------- cmake: copy over git-p4.py for t983[56] perforce test
15:  917a884eb65 <  -:  ----------- CI: add a "linux-cmake-test" to run cmake & ctest on linux