kpatch/LoongArch: fix kernel panic with -fPIC for same-compilation-unit symbol references

Add architecture-specific -fPIC compiler flag for LoongArch64 to prevent
kernel panics when applying livepatches containing references to symbols
defined in the same compilation unit.

Root cause:
In the kpatch workflow, when a function is livepatched, it's extracted
from the original object file and compiled into a separate kernel module.
When the patched function references symbols defined in the same compilation
unit (like 'uts_sem' in kernel/sys.c), these references break if not
compiled as position-independent code.

On LoongArch64, without -fPIC, references to same-compilation-unit symbols
use absolute addressing that assumes fixed memory locations. When the
function is relocated into the livepatch module, these absolute addresses
become invalid, causing kernel panics.

Example failure case:
- SYSCALL_DEFINE1(newuname) references the same-compilation-unit symbol 'uts_sem'
- When kpatch extracts this function into a module, the reference to
  'uts_sem' must be properly relocated
- Without -fPIC, the absolute address reference causes invalid memory
  access and kernel panic

Solution:
Force -fPIC compilation for all LoongArch64 kpatch builds. This ensures
that references to same-compilation-unit symbols use position-independent
addressing, allowing proper relocation by the kernel module loader and
preventing kernel panics in livepatch scenarios.

Co-developed-by: Kexin Liu <liukexin@kylinos.cn>
Singed-off-by: Kexin Liu <liukexin@kylinos.cn>
Signed-off-by: George Guo <guodongtai@kylinos.cn>

Author: George Guo

kpatch-build/kpatch-build

@@ -1288,6 +1288,10 @@ if [[ "$ARCH" = "s390x" ]]; then
 	! kernel_version_gte 6.10.0 && ARCH_KCFLAGS+=" -fPIE"
 fi
 
+if [[ "$ARCH" = "loongarch64" ]]; then
+	ARCH_KCFLAGS="-fPIC"
+fi
+
 export KCFLAGS="-I$DATADIR/patch -ffunction-sections -fdata-sections \
 		$ARCH_KCFLAGS $DEBUG_KCFLAGS"