build: check CMake variable ENABLE_SHARED

Check for the commonly used CMake variable `ENABLE_SHARED` and set
`VBAM_STATIC` accordingly if it is set.

Signed-off-by: Rafael Kitover <rkitover@gmail.com>

cmake/Options.cmake

@@ -22,8 +22,18 @@ elseif(MINGW OR MSYS)
     # Default to static builds on MinGW and all MSYS2 envs.
     set(VBAM_STATIC_DEFAULT ON)
 endif()
+
 option(VBAM_STATIC "Try to link all libraries statically" ${VBAM_STATIC_DEFAULT})
 
+# This is a commonly used CMake option.
+if(DEFINED ENABLE_SHARED)
+   if(NOT ENABLE_SHARED)
+      set(VBAM_STATIC ON)
+   else()
+      set(VBAM_STATIC OFF)
+   endif()
+endif()
+
 if(VBAM_STATIC)
     set(SDL2_STATIC ON)
     set(SDL3_STATIC ON)