fix(curl,qemu): avoid using POSIX character classes for mawk

The POSIX character classes of the form [[:space:]] or [[:lower:]] are
not supported by mawk < 1.3.3-20090727.  For example, this old version
of mawk is still shipped with Ubuntu 18.04 LTS, which offers extended
support until 2028-04.

completions/curl

@@ -105,7 +105,7 @@ _comp_cmd_curl()
         --help | -${noargopts}h)
             local x categories=(
                 $("$1" --help non-existent-category 2>&1 |
-                    _comp_awk '/^[[:space:]]/ {print $1}')
+                    _comp_awk '/^[ \t]/ {print $1}')
             )
             if ((${#categories[@]})); then
                 for x in "${categories[@]}"; do

completions/qemu

@@ -27,13 +27,15 @@ _comp_cmd_qemu()
             return
             ;;
         -soundhw)
-            _comp_compgen_split -- "$("$1" -soundhw help |
-                _comp_awk '/^[[:lower:]]/ {print $1}') all"
+            _comp_compgen_split -- "$("$1" -soundhw help | _comp_awk '
+                function islower(s) { return length(s) > 0 && s == tolower(s); }
+                islower(substr($0, 1, 1)) {print $1}') all"
             return
             ;;
         -machine | -M)
-            _comp_compgen_split -- "$("$1" "$prev" help | _comp_awk \
-                '/^[[:lower:]]/ {print $1}')"
+            _comp_compgen_split -- "$("$1" "$prev" help | _comp_awk '
+                function islower(s) { return length(s) > 0 && s == tolower(s); }
+                islower(substr($0, 1, 1)) {print $1}')"
             return
             ;;
         -cpu)

test/runLint

@@ -22,7 +22,7 @@ gitgrep $cmdstart"awk\b.*-F([[:space:]]|[[:space:]]*[\"'][^\"']{2,})" \
     'awk with -F char or -F ERE, use -Fchar instead (Solaris)'
 
 gitgrep $cmdstart"(_comp_)?awk\b.*\[:[a-z]*:\]" \
-    'awk with POSIX character class not supported in mawk (Debian/Ubuntu)'
+    'awk with POSIX character class not supported in mawk-1.3.3-20090705 (Debian/Ubuntu)'
 
 gitgrep $cmdstart'sed\b.*\\[?+]' \
     'sed with ? or +, use POSIX BRE instead (\{m,n\})'