Reland "[pkg/vm] Handle cross compilation in dart_precompiled_runtime2."

This is a reland of commit 103ffd6

Parent CL adds "aarch64" as a `uname -m` possibility for ARM64.

TEST=manual testing

Original change's description:
> [pkg/vm] Handle cross compilation in dart_precompiled_runtime2.
>
> When cross compiling, use qemu-<arch> to run dartaotruntime for
> the target architecture.
>
> TEST=manual testing with native X64 and cross-compiling ARM64 on X64.
>
> Change-Id: I6ce4e2cfa3108108fe05c7a1fcd2c400a8a47492
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404600
> Reviewed-by: Slava Egorov <[email protected]>
> Commit-Queue: Tess Strickland <[email protected]>

Change-Id: I4407f64e804fbc19d05440ed961a67b5e1c2c047
Cq-Include-Trybots: luci.dart.try:benchmark-linux-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/405761
Reviewed-by: Slava Egorov <[email protected]>
Commit-Queue: Tess Strickland <[email protected]>

Author: sstrickl

pkg/vm/tool/dart_precompiled_runtime2

@@ -23,14 +23,43 @@ PROG_NAME="$(follow_links "$BASH_SOURCE")"
 # Handle the case where dart-sdk/bin has been symlinked to.
 CUR_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"
 
+. "$CUR_DIR/shared_functions.sh"
+
 if [[ `uname` == 'Darwin' ]];
 then
   OUT_DIR="$CUR_DIR"/../../../xcodebuild/
 else
   OUT_DIR="$CUR_DIR"/../../../out/
 fi
 
+HOST_ARCH="$(host_arch)"
+
 export DART_CONFIGURATION=${DART_CONFIGURATION:-ReleaseX64}
+TARGET_ARCH="$(parse_target_arch "$DART_CONFIGURATION")"
 BIN_DIR="$OUT_DIR$DART_CONFIGURATION"
+if [ ! -d "$BIN_DIR" ]; then
+  echo "$BIN_DIR is not a directory" >&2
+  exit 1
+fi
+
+QEMU=""
+# If the target architecture differs from the host architecture, use qemu
+# to run the cross-compiled binary. Cross compilation is denoted by an X
+# between the build mode and the architecture name, re.g., ReleaseXARM64 on X64.
+if [[ "$DART_CONFIGURATION" =~ (Debug|Release|Product)X[^6] ]] && \
+      is_cross_compiled "$HOST_ARCH" "$TARGET_ARCH"; then
+  case "$TARGET_ARCH" in
+    "ARM64")
+    QEMU="qemu-aarch64 -L /usr/aarch64-linux-gnu/"
+    ;;
+    "ARM")
+    QEMU="qemu-arm -L /usr/arm-linux-gnueabihf/"
+    ;;
+    *)
+    echo "No qemu handling for running $TARGET_ARCH binaries on $HOST_ARCH" >&2
+    exit 1
+    ;;
+  esac
+fi
 
-exec "$BIN_DIR"/dartaotruntime "$@"
+exec $QEMU "$BIN_DIR"/dartaotruntime "$@"