Release 2.4.0

Update build flags and some fixes

Makefile: tighten and expand CFLAGS (warnings, std=gnu11, disable PIC/PIE/stack-protector/unwind tables, mcmodel=small), use ld for creating hmkpm.kpm, and remove redundant -O2 from the compile rule.

hmkpm.c: include kconfig.h, bump KPM version to 2.4.0, mark hmkpm_copy_to_kernel_nofault as __maybe_unused, call kp_kconfig_enabled directly (remove weak-null check), and correct STP instruction mask (0xa8000000) used by insn_may_write_reg. These changes improve build correctness and tighten kernel compatibility checks.