coap_openssl.c: Support Microsoft VS builds

Correct reported errors

Update workflow for ms-build to include OpenSSL.

.github/workflows/main.yml

@@ -15,6 +15,7 @@ on:
 env:
   PLATFORM: posix
   TESTS: yes
+  OPENSSL_INSTALL_PATH: C:\Program Files\OpenSSL-Win64\
 
 jobs:
   build-linux:
@@ -112,7 +113,7 @@ jobs:
         run: |
           make -C examples/${{matrix.OS}}
   ms-build:
-    runs-on: windows-2022
+    runs-on: windows-latest
 
     steps:
       - uses: actions/checkout@v2
@@ -120,6 +121,11 @@ jobs:
       - name: Add MSBuild to PATH
         uses: microsoft/setup-msbuild@v1
 
+      - name: Install OpenSSL on Windows (choco)
+        run: |
+          choco install openssl
+        shell: cmd
+
       - name: Build sln
         shell: cmd
         run: call .\scripts\msbuild.sln.cmd