gcc4, gcc6: rebuild against isl24
Bump the pkgrel of gcc4 and gcc6, and regenerate the cross/* versions with "pmbootstrap aportgen gcc6-armv7" etc.
Should fix these errors:
Error loading shared library libisl.so.22: No such file or directory (needed by /usr/gcc6/libexec/gcc/x86_64-alpine-linux-musl/6.4.0/cc1)
Error relocating /usr/gcc6/libexec/gcc/x86_64-alpine-linux-musl/6.4.0/cc1: isl_union_map_free: symbol not found
Error relocating /usr/gcc6/libexec/gcc/x86_64-alpine-linux-musl/6.4.0/cc1: isl_map_from_pw_aff: symbol not found
Error relocating /usr/gcc6/libexec/gcc/x86_64-alpine-linux-musl/6.4.0/cc1: isl_schedule_from_domain: symbol not found
...
Related: https://gitlab.alpinelinux.org/alpine/aports/-/commit/54749a52225575a91f01d04f8d024b4ee853cfb6