Use a consistent rootfs location (#2005)

src/coreclr/build-test.sh

@@ -700,7 +700,7 @@ fi
 if [ $__CrossBuild == 1 ]; then
     export CROSSCOMPILE=1
     if ! [[ -n "$ROOTFS_DIR" ]]; then
-        export ROOTFS_DIR="$__RepoRootDir/eng/common/cross/rootfs/$__BuildArch"
+        export ROOTFS_DIR="$__RepoRootDir/.tools/rootfs/$__BuildArch"
     fi
 fi
 

src/installer/corehost/build.sh

@@ -183,7 +183,7 @@ __cmake_defines="${__cmake_defines} ${__arch_define}"
 # Configure environment if we are doing a cross compile.
 if [ "$__CrossBuild" == 1 ]; then
     if ! [[ -n $ROOTFS_DIR ]]; then
-        export ROOTFS_DIR="$RootRepo/eng/common/cross/rootfs/$__build_arch"
+        export ROOTFS_DIR="$RootRepo/.tools/rootfs/$__build_arch"
     fi
 fi