Ports: Build bc with -std=c17

This port tries to do `UINTMAX_C(true)`.
`UINTMAX_C(x)` is defined as `x ## UL`, resulting in `trueUL` when
using C23's bool keywords.

Ports/bc/package.sh

@@ -8,7 +8,7 @@ useconfigure='true'
 configscript='configure.sh'
 configopts=("--prefix=/usr/local" "--disable-nls")
 
-export CFLAGS='-O3 -flto'
+export CFLAGS='-O3 -flto -std=c17'
 
 configure() {
     run ./"${configscript}" "${configopts[@]}"