toolchain-shar-extract.sh: Ensure sbin directories are in PATH in clean environment

For the PATH host tool whitelisting to work, the sbin directories need to be
in PATH. In the cleaned SDK environment on some distros, this isn't the case
and the SDK would then fail to setup there. This adds code to add such paths
if they do happen to be missing, ugly, but unblocks the PATH whitelisting
which I believe to be important.

(From OE-Core rev: 8c49ab40c2ff2e60b717f479822d1a0021735429)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/files/toolchain-shar-extract.sh

@@ -8,6 +8,20 @@
 [ -f /etc/environment ] && . /etc/environment
 export PATH=`echo "$PATH" | sed -e 's/:\.//' -e 's/::/:/'`
 
+tweakpath () {
+    case ":${PATH}:" in
+        *:"$1":*)
+            ;;
+        *)
+            PATH=$PATH:$1
+    esac
+}
+
+# Some systems don't have /usr/sbin or /sbin in the cleaned environment PATH but we make need it 
+# for the system's host tooling checks
+tweakpath /usr/sbin
+tweakpath /sbin
+
 INST_ARCH=$(uname -m | sed -e "s/i[3-6]86/ix86/" -e "s/x86[-_]64/x86_64/")
 SDK_ARCH=$(echo @SDK_ARCH@ | sed -e "s/i[3-6]86/ix86/" -e "s/x86[-_]64/x86_64/")