Install the mingw import libraries, too.

Patch by Martin Storsjö <martin at martin dot st>

Originally committed as revision 19427 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -1710,7 +1710,9 @@ case $target_os in
         SLIBNAME_WITH_MAJOR='$(SLIBPREF)$(FULLNAME)-$(LIBMAJOR)$(SLIBSUF)'
         SLIB_EXTRA_CMD='-lib.exe /machine:$(LIBTARGET) /def:$$(@:$(SLIBSUF)=.def) /out:$(SUBDIR)$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib)'
         SLIB_INSTALL_EXTRA_CMD='-install -m 644 $(SUBDIR)$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib) "$(SHLIBDIR)/$(SLIBNAME:$(SLIBSUF)=.lib)"; \
-            install -m 644 $(SUBDIR)$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib) "$(SHLIBDIR)/$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib)"'
+            install -m 644 $(SUBDIR)$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib) "$(SHLIBDIR)/$(SLIBNAME_WITH_MAJOR:$(SLIBSUF)=.lib)"; \
+            install -d "$(LIBDIR)"; \
+            install -m 644 $(SUBDIR)lib$(SLIBNAME:$(SLIBSUF)=.dll.a) "$(LIBDIR)/lib$(SLIBNAME:$(SLIBSUF)=.dll.a)"'
         SLIB_UNINSTALL_EXTRA_CMD='rm -f "$(SHLIBDIR)/$(SLIBNAME:$(SLIBSUF)=.lib)"'
         SHFLAGS='-shared -Wl,--output-def,$$(@:$(SLIBSUF)=.def) -Wl,--out-implib,$(SUBDIR)lib$(SLIBNAME:$(SLIBSUF)=.dll.a) -Wl,--enable-runtime-pseudo-reloc -Wl,--enable-auto-image-base'
         objformat="win32"