Add OpenWrt package build and QEMU test scripts

Add OpenWrt SDK packaging under src/Build for console-only x86/64 builds. The build helper prepares the SDK, renders a local package recipe, builds VeraCrypt with the OpenWrt musl toolchain, uses wxWidgets 3.2.10 as static wxBase, enables FUSE3, and skips release self-tests during cross compilation.

Add a package template that installs the console binary, mount.veracrypt, and license files only. The package declares bash for mount.veracrypt and keeps runtime dependencies focused on the direct userland requirements.

Add a documented QEMU runtime test path that boots the matching OpenWrt image, installs the locally built package set with opkg, runs the VeraCrypt version and algorithm self-tests, and exercises a small filesystem=none container mount/unmount flow.

Allow wxbuild callers to pass WX_CONFIGURE_EXTRA_FLAGS so OpenWrt cross configure flags can be passed into the wxWidgets build without carrying an OpenWrt-specific source patch.

src/Makefile

@@ -19,6 +19,8 @@
 # NOTEST:		Do not test release binary
 # RESOURCEDIR:	Run-time resource directory
 # VERBOSE:		Enable verbose messages
+# WITHFUSE3:		Build with FUSE3 support instead of FUSE2
+# WX_CONFIGURE_EXTRA_FLAGS:	Extra flags passed to wxWidgets configure
 # WXSTATIC:		Use static wxWidgets library
 # SSSE3:		Enable SSSE3 support in compiler
 # SSE41:		Enable SSE4.1 support in compiler
@@ -736,7 +738,7 @@ endif
 			WX_CONFIGURE_LEGACY_FLAGS="$$WX_CONFIGURE_LEGACY_FLAGS --enable-$$option"; \
 		fi; \
 	done; \
-	"$(WX_ROOT)/configure" $(WX_CONFIGURE_FLAGS) $$WX_CONFIGURE_LEGACY_FLAGS >/dev/null
+	"$(WX_ROOT)/configure" $(WX_CONFIGURE_FLAGS) $(WX_CONFIGURE_EXTRA_FLAGS) $$WX_CONFIGURE_LEGACY_FLAGS >/dev/null
 
 	@echo Building wxWidgets library...
 	cd "$(WX_BUILD_DIR)" && $(MAKE) -j 4