POSIX compliance: (most) shell scripts converted to generic shell

Ports/.port_include.sh, Toolchain/BuildIt.sh, Toolchain/UseIt.sh
have been left largely untouched due to use of Bash-exclusive
functions and variables such as $BASH_SOURCE, pushd and popd.

Libraries/LibHTML/Scripts/GenerateStyleSheetSource.sh

@@ -1,10 +1,8 @@
-#!/bin/bash
+#!/bin/sh
 
 echo "extern const char $1[];"
 echo "const char $1[] = \"\\"
-IFS=$'\n'
-for line in $(cat $2); do
-    echo $line"\\"
+grep -v '^ *#' < "$2" | while IFS= read -r line; do
+  echo "$line""\\"
 done
 echo "\";"
-