cmake: add support for RV32E targets

Tier 3 no-std targets that require building core and alloc from source.

Signed-off-by: Marcin Szymczyk <[email protected]>

Author: masz-nordic

CMakeLists.txt

@@ -66,10 +66,14 @@ function(_rust_map_target)
         set(RUST_TARGET "${RUST_TARGET}c")
       endif()
       set(RUST_TARGET "${RUST_TARGET}-unknown-none-elf" PARENT_SCOPE)
-    elseif(CONFIG_RISCV_ISA_RV32I)
+    elseif(CONFIG_RISCV_ISA_RV32I OR CONFIG_RISCV_ISA_RV32E)
       # We have multiple choices, try to pick the best.
       # Note that Rust currently only supports subsets of "riscv32imafc" targets!
-      set(RUST_TARGET "riscv32i")
+      if(CONFIG_RISCV_ISA_RV32I)
+        set(RUST_TARGET "riscv32i")
+      else()
+        set(RUST_TARGET "riscv32e")
+      endif()
       if(CONFIG_RISCV_ISA_EXT_M)
         set(RUST_TARGET "${RUST_TARGET}m")
       endif()