Fix VPX not supporting creation of dll
Modified version of https://aur.archlinux.org/cgit/aur.git/tree/configure.patch?h=mingw-w64-libvpx&id=6d658aa0f4d8409fcbd0f20be2c0adcf1e81a297

diff -ruN libvpx/build/make/configure.sh patched/build/make/configure.sh
--- libvpx/build/make/configure.sh	2019-02-13 16:56:48.972857636 +0100
+++ patched/build/make/configure.sh	2019-02-13 16:50:37.995967583 +0100
@@ -1426,11 +1426,13 @@
         win32)
           add_asflags -f win32
           enabled debug && add_asflags -g cv8
+          add_ldflags "-Wl,-no-undefined"
           EXE_SFX=.exe
           ;;
         win64)
           add_asflags -f win64
           enabled debug && add_asflags -g cv8
+          add_ldflags "-Wl,-no-undefined"
           EXE_SFX=.exe
           ;;
         linux*|solaris*|android*)
diff -ruN libvpx/build/make/Makefile patched/build/make/Makefile
--- libvpx/build/make/Makefile	2019-02-13 16:56:48.972857636 +0100
+++ patched/build/make/Makefile	2019-02-13 16:50:37.995967583 +0100
@@ -304,6 +304,7 @@
 	$(if $(quiet),@echo "    [LD] $$@")
 	$(qexec)$$(LD) -shared $$(LDFLAGS) \
             -Wl,--no-undefined -Wl,-soname,$$(SONAME) \
+            -Wl,-out-implib,libvpx.dll.a \
             -Wl,--version-script,$$(EXPORTS_FILE) -o $$@ \
             $$(filter %.o,$$^) $$(extralibs)
 endef
@@ -388,7 +389,7 @@
 .libs: $(LIBS)
 	@touch $@
 $(foreach lib,$(filter %_g.a,$(LIBS)),$(eval $(call archive_template,$(lib))))
-$(foreach lib,$(filter %so.$(SO_VERSION_MAJOR).$(SO_VERSION_MINOR).$(SO_VERSION_PATCH),$(LIBS)),$(eval $(call so_template,$(lib))))
+$(foreach lib,$(filter %dll,$(LIBS)),$(eval $(call so_template,$(lib))))
 $(foreach lib,$(filter %$(SO_VERSION_MAJOR).dylib,$(LIBS)),$(eval $(call dl_template,$(lib))))
 $(foreach lib,$(filter %$(SO_VERSION_MAJOR).dll,$(LIBS)),$(eval $(call dll_template,$(lib))))
 
diff -ruN libvpx/configure patched/configure
--- libvpx/configure	2019-02-13 16:56:49.162860897 +0100
+++ patched/configure	2019-02-13 16:53:03.328719607 +0100
@@ -513,23 +513,23 @@
 }
 
 process_detect() {
-    if enabled shared; then
+    #if enabled shared; then
         # Can only build shared libs on a subset of platforms. Doing this check
         # here rather than at option parse time because the target auto-detect
         # magic happens after the command line has been parsed.
-        case "${tgt_os}" in
-        linux|os2|solaris|darwin*|iphonesimulator*)
+    #    case "${tgt_os}" in
+    #    linux|os2|solaris|darwin*|iphonesimulator*)
             # Supported platforms
-            ;;
-        *)
-            if enabled gnu; then
-                echo "--enable-shared is only supported on ELF; assuming this is OK"
-            else
-                die "--enable-shared only supported on ELF, OS/2, and Darwin for now"
-            fi
-            ;;
-        esac
-    fi
+    #        ;;
+    #    *)
+    #        if enabled gnu; then
+    #            echo "--enable-shared is only supported on ELF; assuming this is OK"
+    #        else
+    #            die "--enable-shared only supported on ELF, OS/2, and Darwin for now"
+    #        fi
+    #        ;;
+    #    esac
+    #fi
     if [ -z "$CC" ] || enabled external_build; then
         echo "Bypassing toolchain for environment detection."
         enable_feature external_build
diff -ruN libvpx/examples.mk patched/examples.mk
--- libvpx/examples.mk	2019-02-13 16:56:49.162860897 +0100
+++ patched/examples.mk	2019-02-13 16:50:37.995967583 +0100
@@ -315,7 +315,7 @@
 ifneq ($(filter os2%,$(TGT_OS)),)
 SHARED_LIB_SUF=_dll.a
 else
-SHARED_LIB_SUF=.so
+SHARED_LIB_SUF=.dll.a
 endif
 endif
 CODEC_LIB_SUF=$(if $(CONFIG_SHARED),$(SHARED_LIB_SUF),.a)
diff -ruN libvpx/libs.mk patched/libs.mk
--- libvpx/libs.mk	2019-02-13 16:56:48.972857636 +0100
+++ patched/libs.mk	2019-02-13 16:50:37.995967583 +0100
@@ -256,12 +256,12 @@
 LIBVPX_SO_SYMLINKS      :=
 LIBVPX_SO_IMPLIB        := libvpx_dll.a
 else
-LIBVPX_SO               := libvpx.so.$(SO_VERSION_MAJOR).$(SO_VERSION_MINOR).$(SO_VERSION_PATCH)
-SHARED_LIB_SUF          := .so
+LIBVPX_SO               := libvpx.dll
+SHARED_LIB_SUF          := .dll
 EXPORT_FILE             := libvpx.ver
-LIBVPX_SO_SYMLINKS      := $(addprefix $(LIBSUBDIR)/, \
-                             libvpx.so libvpx.so.$(SO_VERSION_MAJOR) \
-                             libvpx.so.$(SO_VERSION_MAJOR).$(SO_VERSION_MINOR))
+LIBVPX_SO_SYMLINKS      :=
+
+
 endif
 endif
 endif
@@ -271,7 +271,7 @@
                            $(if $(LIBVPX_SO_IMPLIB), $(BUILD_PFX)$(LIBVPX_SO_IMPLIB))
 $(BUILD_PFX)$(LIBVPX_SO): $(LIBVPX_OBJS) $(EXPORT_FILE)
 $(BUILD_PFX)$(LIBVPX_SO): extralibs += -lm
-$(BUILD_PFX)$(LIBVPX_SO): SONAME = libvpx.so.$(SO_VERSION_MAJOR)
+$(BUILD_PFX)$(LIBVPX_SO): SONAME = libvpx.dll
 $(BUILD_PFX)$(LIBVPX_SO): EXPORTS_FILE = $(EXPORT_FILE)
 
 libvpx.def: $(call enabled,CODEC_EXPORTS)