rust: Build rust backend

In llvm11 we have both riscv32 or riscv64 backends so enable them

Signed-off-by: Khem Raj <raj.khem@gmail.com>

recipes-devtools/rust/rust-llvm.inc

@@ -19,7 +19,7 @@ LLVM_DIR = "llvm${LLVM_RELEASE}"
 
 EXTRA_OECMAKE = " \
     -DCMAKE_BUILD_TYPE=Release \
-    -DLLVM_TARGETS_TO_BUILD='X86;ARM;AArch64;PowerPC;Mips' \
+    -DLLVM_TARGETS_TO_BUILD='ARM;AArch64;Mips;PowerPC;RISCV;X86' \
     -DLLVM_BUILD_DOCS=OFF \
     -DLLVM_ENABLE_TERMINFO=OFF \
     -DLLVM_ENABLE_ZLIB=OFF \