lxc: prepare for llvm 21

[DavidKorczynski]

ref:
#13915 (comment)

[DavidKorczynski]

@evverx are you okay with this? This is the issue we're hitting with llvm 21:

Step #23 - "compile-libfuzzer-address-x86_64": �[31mFAILED: [code=1] �[0msrc/lxc/liblxc.a.p/uuid.c.o 
Step #23 - "compile-libfuzzer-address-x86_64": clang -Isrc/lxc/liblxc.a.p -Isrc/lxc -I../src/lxc -I. -I.. -Isrc -I../src -Isrc/include -I../src/include -I../src/lxc/cgroups -I../src/lxc/storage -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=gnu11 -O0 -g -Wno-format-signedness -Wno-missing-field-initializers -Wno-unused-parameter -Wvla -Wcast-align -Wstrict-prototypes -fno-strict-aliasing -fstack-clash-protection --param=ssp-buffer-size=4 -Werror=implicit-function-declaration -Wmissing-include-dirs -Wold-style-definition -Winit-self -Wunused-but-set-variable -Wno-unused-parameter -Wfloat-equal -Werror=return-type -Werror=incompatible-pointer-types -Wformat=2 -Wshadow -Wendif-labels -Werror=overflow -fdiagnostics-show-option -Werror=shift-count-overflow -Wdate-time -Wnested-externs -fasynchronous-unwind-tables -fexceptions -Warray-bounds -Wreturn-local-addr -Wno-typedef-redefinition -Wno-gnu-variable-sized-type-not-at-end -ffat-lto-objects -include config.h -O1 -fno-omit-frame-pointer -gline-tables-only -Wno-error=incompatible-function-pointer-types -Wno-error=int-conversion -Wno-error=deprecated-declarations -Wno-error=implicit-function-declaration -Wno-error=implicit-int -Wno-error=unknown-warning-option -Wno-error=vla-cxx-extension -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -fPIC -pthread -fvisibility=default -DIN_LIBLXC -MD -MQ src/lxc/liblxc.a.p/uuid.c.o -MF src/lxc/liblxc.a.p/uuid.c.o.d -o src/lxc/liblxc.a.p/uuid.c.o -c ../src/lxc/uuid.c
Step #23 - "compile-libfuzzer-address-x86_64": �[1m../src/lxc/uuid.c:77:32: �[0m�[0;1;31merror: �[0m�[1minitializer-string for character array is too long, array size is 16 but initializer has size 17 (including the null terminating character); did you mean to use the 'nonstring' attribute? [-Werror,-Wunterminated-string-initialization]�[0m
Step #23 - "compile-libfuzzer-address-x86_64":    77 |         �[0;34mstatic�[0m �[0;34mconst�[0m �[0;34mchar�[0m table[�[0;32m16�[0m] = �[0;32m"0123456789abcdef"�[0m;�[0m
Step #23 - "compile-libfuzzer-address-x86_64":       | �[0;1;32m                                      ^~~~~~~~~~~~~~~~~~
Step #23 - "compile-libfuzzer-address-x86_64": �[0m1 error generated.
Step #23 - "compile-libfuzzer-address-x86_64": [31/75] clang -Isrc/lxc/liblxc.a.p -Isrc/lxc -I../src/lxc -I. -I.. -Isrc -I../src -Isrc/include -I../src/include -I../src/lxc/cgroups -I../src/lxc/storage -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -Wextra -Werror -std=gnu11 -O0 -g -Wno-format-signedness -Wno-missing-field-initializers -Wno-unused-parameter -Wvla -Wcast-align -Wstrict-prototypes -fno-strict-aliasing -fstack-clash-protection --param=ssp-buffer-size=4 -Werror=implicit-function-declaration -Wmissing-include-dirs -Wold-style-definition -Winit-self -Wunused-but-set-variable -Wno-unused-parameter -Wfloat-equal -Werror=return-type -Werror=incompatible-pointer-types -Wformat=2 -Wshadow -Wendif-labels -Werror=overflow -fdiagnostics-show-option -Werror=shift-count-overflow -Wdate-time -Wnested-externs -fasynchronous-unwind-tables -fexceptions -Warray-bounds -Wreturn-local-addr -Wno-typedef-redefinition -Wno-gnu-variable-sized-type-not-at-end -ffat-lto-objects -include config.h -O1 -fno-omit-frame-pointer -gline-tables-only -Wno-error=incompatible-function-pointer-types -Wno-error=int-conversion -Wno-error=deprecated-declarations -Wno-error=implicit-function-declaration -Wno-error=implicit-int -Wno-error=unknown-warning-option -Wno-error=vla-cxx-extension -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION -fsanitize=address -fsanitize-address-use-after-scope -fsanitize=fuzzer-no-link -fPIC -pthread -fvisibility=default -DIN_LIBLXC -MD -MQ src/lxc/liblxc.a.p/.._include_strlcat.c.o -MF src/lxc/liblxc.a.p/.._include_strlcat.c.o.d -o src/lxc/liblxc.a.p/.._include_strlcat.c.o -c ../src/include/strlcat.c

[evverx]

I saw that build failure and opened lxc/lxc#4580. I think it would be better to ask @mihalicyn if the lxc project is OK with suppressing that warning for now. My understanding is that it unblocks the LLVM bump so personally I think it's fine to suppress it for the time being.