rust: set _bootstrapping=no for all architectures (not just aarch64)

when _bootstrapping=no, the rust build is configured to use the local rust for stage 0.
stage 0 will use the installed MSYS2 rust (must be the latest version...).

when _bootstrapping=yes, the build is configured to download and extract the previous rust version.
in this case, the official rust build will be used which kind of defeats the point (?)

mingw-w64-rust/PKGBUILD

@@ -4,7 +4,11 @@
 # Contributor: Philippe Renon <[email protected]>
 
 _realname=rust
-_bootstrapping=yes
+# when _bootstrapping=no, the rust build is configured to use the local rust for stage 0
+# stage 0 will use the installed MSYS2 rust (hopefully the latest version...)
+# when _bootstrapping=yes, the build is configured to download and extract the previous rust version
+# in this case, the official rust build will be used which kind of defeats the point (?)
+_bootstrapping=no
 if [[ $MINGW_PACKAGE_PREFIX == *-clang-aarch64 ]]; then
   _bootstrapping=no
 fi