rts: remove -Wl,-U,___darwin_check_fd_set_overflow hack

This patch bumps macOS minimum SDK version to 11.0 for x86_64-darwin
to align it with aarch64-darwin. This allows us to get rid of the
horrible -Wl,-U,___darwin_check_fd_set_overflow hack, which is causing
linker warnings and testsuite failures on macOS 15. Fixes #25504.

(cherry picked from commit 88c4fe1d)
(cherry picked from commit 5c7e7695)