Build Windows libsndfile dynamically, but dependencies statically

this used to work, but I broke it on accident. This commit also adds
support for arm64 builds, which were not previously available.

.github/workflows/build-libs.yml

@@ -104,14 +104,14 @@ jobs:
     strategy:
       matrix:
         include:
-          - triplet: "x64-windows"
+          # see ./triplets/README.md for info on "custom" triplets:
+          - triplet: "x64-windows-custom"
             libname: "libsndfile_x64.dll"
-          - triplet: "x86-windows"
+          - triplet: "x86-windows-custom"
             libname: "libsndfile_x86.dll"
-          - triplet: "arm64-windows"
+          - triplet: "arm64-windows-custom"
             libname: "libsndfile_arm64.dll"
       fail-fast: true
-
     steps:
       - uses: actions/checkout@v3
       - name: Update VCPKG

triplets/README.md

@@ -1,4 +1,7 @@
-Custom triplets for Vcpkg.
+VCPKG allows either, static builds, or dynamic builds. However, we need to 
+build libsndfile as a dynamic library, but its dependencies should be 
+statically linked.
 
-https://vcpkg.readthedocs.io/en/latest/users/triplets/
-https://vcpkg.readthedocs.io/en/latest/examples/overlay-triplets-linux-dynamic/
+These custom triplets accomplish this. They are a copy of the official
+{arm64,x64,x86}-windows triplets at https://github.com/microsoft/vcpkg/tree/master/triplets,
+but with all libraries except libsndfile configured for static linkage.

triplets/arm64-windows-custom.cmake

@@ -0,0 +1,7 @@
+set(VCPKG_TARGET_ARCHITECTURE arm64)
+set(VCPKG_CRT_LINKAGE dynamic)
+set(VCPKG_LIBRARY_LINKAGE static)
+
+if (PORT MATCHES "libsndfile")
+	set(VCPKG_LIBRARY_LINKAGE dynamic)
+endif()

triplets/x64-windows-custom.cmake

@@ -1,8 +1,6 @@
 set(VCPKG_TARGET_ARCHITECTURE x64)
 set(VCPKG_CRT_LINKAGE dynamic)  # Runtime always dynamically linked.
 set(VCPKG_LIBRARY_LINKAGE static)  # Libs are static by default.
-set(VCPKG_PLATFORM_TOOLSET v140)  # Enforce v140 toolset.
-set(VCPKG_BUILD_TYPE release)  # Skip debug builds.
 
 if (PORT STREQUAL libsndfile)  # Only libsndfile is dynamic.
 	set(VCPKG_LIBRARY_LINKAGE dynamic)

triplets/x86-windows-custom.cmake

@@ -1,8 +1,6 @@
 set(VCPKG_TARGET_ARCHITECTURE x86)
 set(VCPKG_CRT_LINKAGE dynamic)
 set(VCPKG_LIBRARY_LINKAGE static)
-set(VCPKG_PLATFORM_TOOLSET v140)
-set(VCPKG_BUILD_TYPE release)
 
 if (PORT STREQUAL libsndfile)
 	set(VCPKG_LIBRARY_LINKAGE dynamic)