meson: enable -Warray-bounds and -fstrict-flex-arrays

-fstrict-flex-arrays means that the compiler doesn't have to assume that any
trailing array is a flex array. I.e. unless the array is declared without a
specified size, only indices in the declared range are valid.

-Warray-bounds turns on the warnings about out-of-bounds array accesses.
-Warray-bounds=2 does some more warnings, with higher false positive rate. But
it doesn't seem to yield any false positives in our codebase, so enable it.

clang supports -Warray-bounds, but not -Warray-bounds=2.
gcc supports both.
gcc-13 supports -fstrict-flex-arrays.

See https://people.kernel.org/kees/bounded-flexible-arrays-in-c for a long
discussion of use in the kernel.

meson.build

@@ -354,6 +354,8 @@ basic_disabled_warnings = [
 ]
 
 possible_common_cc_flags = [
+        '-Warray-bounds',     # clang
+        '-Warray-bounds=2',
         '-Wdate-time',
         '-Wendif-labels',
         '-Werror=format=2',
@@ -391,6 +393,8 @@ possible_common_cc_flags = [
         # negative arguments are correctly detected starting with meson 0.46.
         '-Wno-error=#warnings',  # clang
         '-Wno-string-plus-int',  # clang
+
+        '-fstrict-flex-arrays',
 ]
 
 c_args = get_option('c_args')