MSVC: Teach find_library to consider the 'libfoo.a' naming convention

When targeting the GNU ABI, we consider `.a` libraries first but also
accept `.lib`.  For symmetry, when targeting the MSVC ABI, we now
consider `.lib` first but also accept `.a`.

This adds support for meson-generated static libraries, which are named
with the pattern `lib${foo}.a`:

* https://mesonbuild.com/FAQ.html#why-does-building-my-project-with-msvc-output-static-libraries-called-libfooa

Note that this was previously attempted by

* commit be848a71b0 (MSVC: Teach find_library to consider the 'libfoo.a'
                     naming convention, 2022-09-19, v3.25.0-rc1~111^2)

but was reverted by

* commit 955d6245c1 (MSVC: Revert "Teach find_library to consider the
                     'libfoo.a' naming convention", 2022-11-28, v3.25.1~6^2)

due to problems finding GNU ABI libraries in PATH-derived prefixes.
Since then,

* commit 0a81110b84 (find_(library|file|path): Drop PATH-derived search
                     prefixes, 2023-09-14, v3.28.0-rc1~91^2)

removed the problematic search paths, so we can restore this change.

Fixes: #23975

Help/release/dev/find_library-msvc-libfoo.a.rst

@@ -0,0 +1,7 @@
+find_library-msvc-libfoo.a
+--------------------------
+
+* On Windows, when targeting the MSVC ABI, the :command:`find_library` command
+  now accepts ``.a`` file names after first considering ``.lib``.  This is
+  symmetric with existing behavior when targeting the GNU ABI, in which the
+  command accepts ``.lib`` file names after first considering ``.a``.

Modules/Platform/Windows.cmake

@@ -13,10 +13,14 @@ set(CMAKE_LINK_LIBRARY_SUFFIX ".lib")
 set(CMAKE_DL_LIBS "")
 set(CMAKE_EXTRA_LINK_EXTENSIONS ".targets")
 
-set(CMAKE_FIND_LIBRARY_PREFIXES "")
+set(CMAKE_FIND_LIBRARY_PREFIXES
+  "" # static or import library from MSVC tooling
+  "lib" # static library from Meson with MSVC tooling
+  )
 set(CMAKE_FIND_LIBRARY_SUFFIXES
   ".dll.lib" # import library from Rust toolchain for MSVC ABI
   ".lib" # static or import library from MSVC tooling
+  ".a" # static library from Meson with MSVC tooling
   )
 
 # for borland make long command lines are redirected to a file

Tests/RunCMake/find_library/Windows-MSVC-stdout.txt

@@ -1,2 +1,3 @@
 -- STATIC_LIBRARY='[^']*/Tests/RunCMake/find_library/Windows-MSVC/static.lib'
+-- MESON_STATIC_LIBRARY='[^']*/Tests/RunCMake/find_library/Windows-MSVC/libmeson_static.a'
 -- RUSTC_IMPORT_LIBRARY='[^']*/Tests/RunCMake/find_library/Windows-MSVC/rustc_import.dll.lib'

Tests/RunCMake/find_library/Windows-MSVC.cmake

@@ -3,5 +3,8 @@ enable_language(C)
 find_library(STATIC_LIBRARY NAMES static NO_DEFAULT_PATH PATHS ${CMAKE_CURRENT_SOURCE_DIR}/Windows-MSVC)
 message(STATUS "STATIC_LIBRARY='${STATIC_LIBRARY}'")
 
+find_library(MESON_STATIC_LIBRARY NAMES meson_static NO_DEFAULT_PATH PATHS ${CMAKE_CURRENT_SOURCE_DIR}/Windows-MSVC)
+message(STATUS "MESON_STATIC_LIBRARY='${MESON_STATIC_LIBRARY}'")
+
 find_library(RUSTC_IMPORT_LIBRARY NAMES rustc_import NO_DEFAULT_PATH PATHS ${CMAKE_CURRENT_SOURCE_DIR}/Windows-MSVC)
 message(STATUS "RUSTC_IMPORT_LIBRARY='${RUSTC_IMPORT_LIBRARY}'")