gcc-15: disable '-Wunterminated-string-initialization' entirely for now

I had left the warning around but as a non-fatal error to get my gcc-15
builds going, but fixed up some of the most annoying warning cases so
that it wouldn't be *too* verbose.

Because I like the _concept_ of the warning, even if I detested the
implementation to shut it up.

It turns out the implementation to shut it up is even more broken than I
thought, and my "shut up most of the warnings" patch just caused fatal
errors on gcc-14 instead.

I had tested with clang, but when I upgrade my development environment,
I try to do it on all machines because I hate having different systems
to maintain, and hadn't realized that gcc-14 now had issues.

The ACPI case is literally why I wanted to have a *type* that doesn't
trigger the warning (see commit d5d45a7: "gcc-15: make
'unterminated string initialization' just a warning"), instead of
marking individual places as "__nonstring".

But gcc-14 doesn't like that __nonstring location that shut gcc-15 up,
because it's on an array of char arrays, not on one single array:

  drivers/acpi/tables.c:399:1: error: 'nonstring' attribute ignored on objects of type 'const char[][4]' [-Werror=attributes]
    399 | static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst __nonstring = {
        | ^~~~~~

and my attempts to nest it properly with a type had failed, because of
how gcc doesn't like marking the types as having attributes, only
symbols.

There may be some trick to it, but I was already annoyed by the bad
attribute design, now I'm just entirely fed up with it.

I wish gcc had a proper way to say "this type is a *byte* array, not a
string".

The obvious thing would be to distinguish between "char []" and an
explicitly signed "unsigned char []" (as opposed to an implicitly
unsigned char, which is typically an architecture-specific default, but
for the kernel is universal thanks to '-funsigned-char').

But any "we can typedef a 8-bit type to not become a string just because
it's an array" model would be fine.

But "__attribute__((nonstring))" is sadly not that sane model.

Reported-by: Chris Clayton <chris2553@googlemail.com>
Fixes: 4b4bd8c ("gcc-15: acpi: sprinkle random '__nonstring' crumbles around")
Fixes: d5d45a7 ("gcc-15: make 'unterminated string initialization' just a warning")
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Makefile

@@ -1056,8 +1056,8 @@ KBUILD_CFLAGS += $(call cc-option, -fstrict-flex-arrays=3)
 KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow)
 KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)
 
-#Currently, disable -Wunterminated-string-initialization as an error
-KBUILD_CFLAGS += $(call cc-option, -Wno-error=unterminated-string-initialization)
+#Currently, disable -Wunterminated-string-initialization as broken
+KBUILD_CFLAGS += $(call cc-option, -Wno-unterminated-string-initialization)
 
 # disable invalid "can't wrap" optimizations for signed / pointers
 KBUILD_CFLAGS	+= -fno-strict-overflow

drivers/acpi/tables.c

@@ -396,7 +396,7 @@ static u8 __init acpi_table_checksum(u8 *buffer, u32 length)
 }
 
 /* All but ACPI_SIG_RSDP and ACPI_SIG_FACS: */
-static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst __nonstring = {
+static const char table_sigs[][ACPI_NAMESEG_SIZE] __initconst = {
 	ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
 	ACPI_SIG_EINJ, ACPI_SIG_ERST, ACPI_SIG_HEST, ACPI_SIG_MADT,
 	ACPI_SIG_MSCT, ACPI_SIG_SBST, ACPI_SIG_SLIT, ACPI_SIG_SRAT,