allow building "ffmpeg.exe"

add new feature "ffmpeg" which allows to build "ffmpeg.exe" - ex. : vcpkg install ffmpeg[x264,gpl,nonfree,ffplay,ffprobe,openssl,lzma,opencl,ffmpeg]:x64-windows-static --recurse

ports/ffmpeg/CONTROL

@@ -3,6 +3,9 @@ Version: 4.1-1
 Description: a library to decode, encode, transcode, mux, demux, stream, filter and play pretty much anything that humans and machines have created.
   FFmpeg is the leading multimedia framework, able to decode, encode, transcode, mux, demux, stream, filter and play pretty much anything that humans and machines have created. It supports the most obscure ancient formats up to the cutting edge. No matter if they were designed by some standards committee, the community or a corporation. It is also highly portable: FFmpeg compiles, runs, and passes our testing infrastructure FATE across Linux, Mac OS X, Microsoft Windows, the BSDs, Solaris, etc. under a wide variety of build environments, machine architectures, and configurations.
 
+Feature: ffmpeg
+Description: build the ffmpeg.exe application
+
 Feature: ffserver
 Description: ffserver appplication support in ffmpeg
 

ports/ffmpeg/fix_windowsinclude-in-ffmpegexe-1.patch

@@ -0,0 +1,11 @@
+--- a/cmdutils.c	2017-07-29 19:49:29.000000000 +0200
++++ b/cmdutils.c	2018-09-02 20:31:42.509408400 +0200
+@@ -62,6 +62,8 @@
+ #include <sys/resource.h>
+ #endif
+ #ifdef _WIN32
++#define _WIN32_WINNT 0x0600
++#define WIN32_LEAN_AND_MEAN
+ #include <windows.h>
+ #endif
+

ports/ffmpeg/fix_windowsinclude-in-ffmpegexe-2.patch

@@ -0,0 +1,14 @@
+--- a/ffmpeg.c	2017-07-29 19:49:29.000000000 +0200
++++ b/ffmpeg.c	2018-09-02 20:32:27.666725200 +0200
+@@ -23,6 +23,11 @@
+  * multimedia converter based on the FFmpeg libraries
+  */
+
++#define _WIN32_WINNT 0x0502	// Must be less than 0x0600, because otherwise WinSock2.h defines "pollfd" which then gets redefined in "os_support.h".
++							// I suppose that "HAVE_STRUCT_POLLFD" should be 1, but it happens to be 0. Sorry, this is somewhat beyond me.
++#define WIN32_LEAN_AND_MEAN
++
++
+ #include "config.h"
+ #include <ctype.h>
+ #include <string.h>

ports/ffmpeg/fix_windowsinclude-in-ffmpegexe-3.patch

@@ -0,0 +1,19 @@
+--- a/ffmpeg_dxva2.c	2017-07-29 19:49:29.000000000 +0200
++++ b/ffmpeg_dxva2.c	2018-09-02 20:33:48.248716100 +0200
+@@ -16,12 +16,14 @@
+  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+  */
+
+-#include <windows.h>
+-
+ #ifdef _WIN32_WINNT
+ #undef _WIN32_WINNT
+ #endif
+ #define _WIN32_WINNT 0x0600
++#define WIN32_LEAN_AND_MEAN
++
++#include <windows.h>
++
+ #define DXVA2API_USE_BITFIELDS
+ #define COBJMACROS
+

ports/ffmpeg/portfile.cmake

@@ -17,6 +17,9 @@ vcpkg_apply_patches(
         ${CMAKE_CURRENT_LIST_DIR}/create-lib-libraries.patch
         ${CMAKE_CURRENT_LIST_DIR}/detect-openssl.patch
         ${CMAKE_CURRENT_LIST_DIR}/configure_opencv.patch
+        ${CMAKE_CURRENT_LIST_DIR}/fix_windowsinclude-in-ffmpegexe-1.patch
+        ${CMAKE_CURRENT_LIST_DIR}/fix_windowsinclude-in-ffmpegexe-2.patch
+        ${CMAKE_CURRENT_LIST_DIR}/fix_windowsinclude-in-ffmpegexe-3.patch
 )
 
 vcpkg_find_acquire_program(YASM)
@@ -36,7 +39,7 @@ set(_csc_PROJECT_PATH ffmpeg)
 
 file(REMOVE_RECURSE ${CURRENT_BUILDTREES_DIR}/${TARGET_TRIPLET}-dbg ${CURRENT_BUILDTREES_DIR}/${TARGET_TRIPLET}-rel)
 
-set(OPTIONS "--enable-asm --enable-yasm --disable-doc --enable-debug --disable-ffmpeg")
+set(OPTIONS "--enable-asm --enable-yasm --disable-doc --enable-debug")
 set(OPTIONS "${OPTIONS} --enable-runtime-cpudetect")
 
 if("nonfree" IN_LIST FEATURES)
@@ -53,6 +56,12 @@ else()
     set(OPTIONS "${OPTIONS} --disable-openssl")
 endif()
 
+if("ffmpeg" IN_LIST FEATURES)
+    set(OPTIONS "${OPTIONS} --enable-ffmpeg")
+else()
+    set(OPTIONS "${OPTIONS} --disable-ffmpeg")
+endif()
+
 if("ffplay" IN_LIST FEATURES)
     set(OPTIONS "${OPTIONS} --enable-ffplay")
 else()