QDMA: linux-kernel: use ccflags-y instead of EXTRA_CFLAGS (fix build on Linux 6.15+/Ubuntu 26.04)

[amd-vserbu]

Summary

Fixes the QDMA Linux kernel driver build on Linux ≥ 6.15, including the Ubuntu 26.04 LTS kernel (7.0). kbuild removed EXTRA_CFLAGS support in 6.15, so the driver's include paths were silently dropped, causing:

In file included from nl.c:27:
libqdma/libqdma_export.h:41:10: fatal error: qdma_access_export.h: No such file or directory
   41 | #include "qdma_access_export.h"
      |          ^~~~~~~~~~~~~~~~~~~~~~
compilation terminated.

Fixes #393

Changes

• QDMA/linux-kernel/driver/src/Makefile: EXTRA_CFLAGS -> ccflags-y
• QDMA/linux-kernel/driver/libqdma/Makefile: EXTRA_CFLAGS -> ccflags-y
• Added -Wno-error=empty-body so -Wall -Werror no longer fails on the empty if body in libqdma/thread.c with newer GCC.

Why ccflags-y

EXTRA_CFLAGS was deprecated in 2007 and removed in Linux 6.15 (torvalds/linux@e966ad0edd00). ccflags-y is the supported replacement and has existed since kernel 2.6.24, so this stays compatible with older kernels.

Note for reviewers

The empty-body case is handled by suppressing -Werror=empty-body. If you'd prefer, the underlying if (detail) ; in libqdma/thread.c can instead be cleaned up directly. Happy to adjust.