update(cmake): Use the static CRT on Windows by default

Set CMAKE_MSVC_RUNTIME_LIBRARY to "MultiThreaded" unless it was set
externally or if we're building shared libs. This

- uses CMake's documented variable to control CRT linking.
- ensures that we use the static CRT by default.
- allows the CRT setting to be overridden.

Add a Windows shared CRT CI job.

Signed-off-by: Gerald Combs <gerald@wireshark.org>

.github/workflows/ci.yml

@@ -160,7 +160,10 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [windows-latest, macos-latest]
+        os: [windows-latest]
+        crt: [MultiThreaded, MultiThreadedDLL]
+        include:
+          - os: macos-latest
     runs-on: ${{ matrix.os }}
     steps:
       - name: Checkout Libs ⤵️
@@ -171,7 +174,7 @@ jobs:
       - name: Build and test 🏗️🧪
         run: |
           mkdir -p build
-          cd build && cmake -DUSE_BUNDLED_DEPS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DCREATE_TEST_TARGETS=ON -DMINIMAL_BUILD=ON ..
+          cd build && cmake -DUSE_BUNDLED_DEPS=ON -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=${{ matrix.crt }} -DCREATE_TEST_TARGETS=ON -DMINIMAL_BUILD=ON ..
           cmake --build . --config Release && make run-unit-tests || libsinsp\test\Release\unit-test-libsinsp.exe
 
   build-shared-libs-macos-amd64:

CMakeLists.txt

@@ -38,7 +38,11 @@ if(POLICY CMP0042)
 	cmake_policy(SET CMP0042 NEW)
 endif()
 
-# Enable CMAKE_MSVC_RUNTIME_LIBRARY on Windows + CMake >= 3.15
+# Enable CMAKE_MSVC_RUNTIME_LIBRARY on Windows + CMake >= 3.15 and link
+# with the static (MultiThreaded) CRT unless instructed otherwise.
+if(NOT (CMAKE_MSVC_RUNTIME_LIBRARY OR BUILD_SHARED_LIBS))
+	set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
+endif()
 if(POLICY CMP0091)
 	cmake_policy(SET CMP0091 NEW)
 endif()