libavutil: Make avpriv_open a library-internal function on msvcrt

Add one copy of the function into each of the libraries, similarly
to what we do for log2_tab. When using static libs, only one
copy of the file_open.o object file gets included, while when
using shared libraries, each of them get a copy of its own.

This fixes DLL builds with a statically linked C runtime, where
each DLL effectively has got its own instance of the C runtime,
where file descriptors can't be shared across runtimes.

On systems not using msvcrt, the function is not duplicated.

Signed-off-by: Martin Storsjö <martin@martin.st>

libavdevice/Makefile

@@ -7,6 +7,8 @@ HEADERS = avdevice.h                                                    \
 OBJS    = alldevices.o                                                  \
           avdevice.o                                                    \
 
+OBJS-$(HAVE_MSVCRT) += file_open.o
+
 # input/output devices
 OBJS-$(CONFIG_ALSA_INDEV)                += alsa-audio-common.o \
                                             alsa-audio-dec.o

libavdevice/file_open.c

@@ -0,0 +1 @@
+#include "libavutil/file_open.c"