export DLLs functions for MSVC with CMake

- Add 3 DEF files to export functions from Windows DLLs
  - Add gettimeofday to crypto/crypto.def (*1)
  - Remove gai_strerrorA from tls/tls.def (*1)
- Fix CMakeLists.txt to use DEF files as PRIVATE
- Change DLL import library file name since it duplicates with static library
- Ignore compiler warning C4267, and Edit CMAKE_C_FLAGS not to overwrite it (*1)
- Add USE_SHARED option to build openssl.exe with shared libraries (*1)

  (*1) recommended by @mcnameej

crypto/Makefile.am

@@ -9,6 +9,7 @@ lib_LTLIBRARIES = libcrypto.la
 
 EXTRA_DIST = VERSION
 EXTRA_DIST += CMakeLists.txt
+EXTRA_DIST += crypto.def
 
 # needed for a CMake target
 EXTRA_DIST += compat/strcasecmp.c