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: 54749a5222
[ci:skip-build]: already built successfully in CI
d34f9020da