bring back setting, some libraries don't build a static version if the shared one should also be built...

src/SPC/builder/unix/library/mimalloc.php

@@ -13,7 +13,7 @@ trait mimalloc
     {
         $cmake = UnixCMakeExecutor::create($this)
             ->addConfigureArgs(
-                '-DMI_BUILD_SHARED=ON',
+                '-DMI_BUILD_SHARED=' . (getenv('SPC_LINK_STATIC') ? 'OFF' : 'ON'),
                 '-DMI_BUILD_OBJECT=OFF',
                 '-DMI_INSTALL_TOPLEVEL=ON',
             );