Fix bash issues in osx_cc_wrapper.sh.tpl (#685)

This PR fixes two issues with the `osx_cc_wrapper.sh.tpl` and
`cc_wrapper.sh.tpl` templates:

1. (Both files) The condition for entering the loop to process parameter
files included `-r ${i:1}`, which was checking the loop index value, not
the argument that corresponds to the name of the parameter file. This
was changed to `-r ${!i:1}`.
2. (Only `osx_cc_wrapper.sh.tpl`) The temporary file was being appended
to with the result of `parse_option`, which doesn't return any value,
resulting in the tempfile being empty. This was changed to run
`parse_option "${opt}"` separately from appending the option to the
file, ensuring that the temporary file is being populated with the
sanitized commands.

The first fix addresses the issue of arguments in the param files not
being sanitized, while the second addresses the issue of the sanitized
arguments in the parameter file not being passed through.

---------

Co-authored-by: Trevor Elliott <trevor@stripe.com>

Author: elliottt

toolchain/cc_wrapper.sh.tpl

@@ -118,7 +118,7 @@ function sanitize_option() {
 
 cmd=()
 for ((i = 0; i <= $#; i++)); do
-  if [[ ${!i} == @* && -r "${i:1}" ]]; then
+  if [[ ${!i} == @* && -r "${!i:1}" ]]; then
     # Create a new, sanitized file.
     tmpfile=$(mktemp)
     CLEANUP_FILES+=("${tmpfile}")

toolchain/osx_cc_wrapper.sh.tpl

@@ -146,15 +146,16 @@ function sanitize_option() {
 
 cmd=()
 for ((i = 0; i <= $#; i++)); do
-  if [[ ${!i} == @* && -r "${i:1}" ]]; then
+  if [[ ${!i} == @* && -r "${!i:1}" ]]; then
     tmpfile=$(mktemp)
     CLEANUP_FILES+=("${tmpfile}")
     while IFS= read -r opt; do
       opt="$(
         set -e
         sanitize_option "${opt}"
       )"
-      parse_option "${opt}" >>"${tmpfile}"
+      parse_option "${opt}"
+      echo "${opt}" >>"${tmpfile}"
     done <"${!i:1}"
     cmd+=("@${tmpfile}")
   else