autosetup-find-tclsh: Quote CC_FOR_BUILD to prevent word splitting

In some build environments, CC_FOR_BUILD can include essential compiler
flags. For example, in Guix it may have a value such as:
`/gnu/store/10krix03rl5hqjv2c0qmj44ic9bgd8rc-gcc-toolchain-13.3.0/bin/gcc -isystem /gnu/store/10krix03rl5hqjv2c0qmj44ic9bgd8rc-gcc-toolchain-13.3.0/include`

See upstream: https://github.com/msteveb/autosetup/pull/81.


--- a/autosetup/autosetup-find-tclsh
+++ b/autosetup/autosetup-find-tclsh
@@ -8,7 +8,7 @@
 	{ $tclsh "$d/${1-autosetup-test-tclsh}"; } 2>/dev/null && exit 0
 done
 echo 1>&2 "No installed jimsh or tclsh, building local bootstrap jimsh0"
-for cc in ${CC_FOR_BUILD:-cc} gcc; do
+for cc in "${CC_FOR_BUILD:-cc}" gcc; do
 	{ $cc -o jimsh0 "$d/jimsh0.c"; } 2>/dev/null >/dev/null || continue
 	./jimsh0 "$d/${1-autosetup-test-tclsh}" && exit 0
 done