[sanitizer_common] Fix build breakage by guarding #include <dlfcn.h>

My change
(https://github.com/llvm/llvm-project/commit/0be4c6b9483594494051e8f1f67afc2b516270ca) broke the Windows buildbot
(https://lab.llvm.org/buildbot/#/builders/127/builds/57976/steps/4/logs/stdio)

This fixes forward by adding a guard