turns out mingw does actually produce .a libs and not .dll.a

external/CMakeLists.txt

@@ -116,7 +116,6 @@ IF(!UNBOUND_INCLUDE_DIR OR STATIC)
       LOG_TEST 1
       LOG_INSTALL 1
     )
-    set(UNBOUND_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/unbound/src/libunbound-build/libunbound.dll.a;${OPENSSL_LIBRARIES}" PARENT_SCOPE)
   ELSEIF(APPLE)
     execute_process(COMMAND brew --prefix OUTPUT_VARIABLE BREW_PREFIX OUTPUT_STRIP_TRAILING_WHITESPACE)
     EXTERNALPROJECT_ADD(
@@ -135,7 +134,6 @@ IF(!UNBOUND_INCLUDE_DIR OR STATIC)
       LOG_TEST 1
       LOG_INSTALL 1
     )
-    set(UNBOUND_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/unbound/src/libunbound-build/libunbound.a;${OPENSSL_LIBRARIES}" PARENT_SCOPE)
   ELSE()
     EXTERNALPROJECT_ADD(
       libunbound
@@ -153,11 +151,11 @@ IF(!UNBOUND_INCLUDE_DIR OR STATIC)
       LOG_TEST 1
       LOG_INSTALL 1
     )
-    set(UNBOUND_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/unbound/src/libunbound-build/libunbound.a;${OPENSSL_LIBRARIES}" PARENT_SCOPE)
   ENDIF()
   
   set(UNBOUND_STATIC true PARENT_SCOPE)
   set(UNBOUND_INCLUDE "${CMAKE_CURRENT_BINARY_DIR}/unbound/src/libunbound-build" PARENT_SCOPE)
+  set(UNBOUND_LIBRARY "${CMAKE_CURRENT_BINARY_DIR}/unbound/src/libunbound-build/libunbound.a;${OPENSSL_LIBRARIES}" PARENT_SCOPE)
 ELSE()
   MESSAGE(STATUS "Found libunbound include (unbound.h) in ${UNBOUND_INCLUDE_DIR}")
   IF(UNBOUND_LIBRARIES)