lang/rust: Disable static linking against libstdc++

 - According to the PR below and due to some llvm-tools
   and bootstrap untangling, the default was made to link
   statically against libstdc++, although it can be opted-out:
   rust-lang/rust#94832
 - Our static libstdc++ is not compiled with -fPIC apparently
   (dunno why) so it's not possible to do the static linking
   against it when other libraries are compiled with -fPIC.
   There is probably more to it though.

Pointed-out-by: jynelson (rust's discord)

ports/lang/rust/diffs/Makefile.diff

@@ -1,6 +1,6 @@
---- Makefile.orig	2022-01-20 00:07:08 UTC
+--- Makefile.orig	2022-07-26 22:50:42 UTC
 +++ Makefile
-@@ -92,10 +92,6 @@ _CARGO_BOOTSTRAP=	${BOOTSTRAPS_DATE_${AR
+@@ -105,10 +105,6 @@ SHEBANG_FILES=		compiler/rustc_codegen_c
 
  .include <bsd.port.pre.mk>
 
@@ -11,3 +11,11 @@
  .if ${ARCH} == powerpc
  # bfd to link rustc_driver; lld currently can't
  BUILD_DEPENDS+=	ld.bfd:devel/binutils
+@@ -229,6 +225,7 @@ do-configure:
+ 	@${ECHO_CMD} 'ccache=false' >> ${WRKSRC}/config.toml
+ .endif
+ 	@${ECHO_CMD} 'ninja=true' >> ${WRKSRC}/config.toml
++	@${ECHO_CMD} 'static-libstdcpp=false' >> ${WRKSRC}/config.toml
+ .if ${ARCH} == powerpc
+ # Rust doesn't call the system compiler with the full version of the target.
+ # This makes powerpc miscompile due to the secure-plt ABI change.