Changed curl.dll to libcurl.dll.

  add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for

  dynamic import symbols. If you get linker error like "unknown symbol

  __imp__curl_easy_init ..." you have linked against the wrong (static)

  library.  If you want to use the curl.dll and import lib, you don't need any

  extra CFLAGS, but use one of the import libraries below. These are the

  library.  If you want to use the libcurl.dll and import lib, you don't need

  any extra CFLAGS, but use one of the import libraries below. These are the

  libraries produced by the various lib/Makefile.* files:

  Target:          static lib.   import lib for curl*.dll.

  --------------------------------------------------------

  Target:          static lib.   import lib for libcurl*.dll.

  -----------------------------------------------------------

  MingW:           libcurl.a     libcurldll.a

  MSVC (release):  libcurl.lib   libcurl_imp.lib

  MSVC (debug):    libcurld.lib  libcurld_imp.lib