make sure that find_sysroot always sets MIRI_SYSROOT

Author: RalfJung

miri

@@ -55,7 +55,6 @@ build_sysroot() {
     cargo run $CARGO_BUILD_FLAGS --bin cargo-miri -- miri setup "$@"
     # Call again, to just set env var.
     eval $(cargo run $CARGO_BUILD_FLAGS -q --bin cargo-miri -- miri setup --env "$@")
-    export MIRI_SYSROOT
 }
 
 # Prepare and set MIRI_SYSROOT.  Respects `MIRI_TEST_TARGET` and takes into account
@@ -73,7 +72,7 @@ find_sysroot() {
             build_sysroot --target "$MIRI_TEST_TARGET"
         else
             # Assume we have a proper host libstd in $SYSROOT.
-            true
+            MIRI_SYSROOT="$SYSROOT"
         fi
     else
         # A normal toolchain.  We have to build a sysroot either way.
@@ -83,6 +82,7 @@ find_sysroot() {
             build_sysroot
         fi
     fi
+    export MIRI_SYSROOT
 }
 
 ## Main