meson: detect and use __attribute__((no_reorder))

In some builds (package builds, so with optimization and lto, but I
haven't been able to pin down the exact combination on options that
matters), we end up with items in the verbs array reordered. The order
matters (because of groups, but also because we have some specific order
for display), so this reordering is something that we don't want.

From what I was able to read, the compiler + linker generally keep the
order within a single translation unit, but this is more of a convention
and implementation choice than a guarantee. Add this attribute [1]. It
seems to have the desired effect in CI.

[1] https://gcc.gnu.org/onlinedocs/gcc-15.2.0/gcc/Common-Function-Attributes.html#index-no_005freorder-function-attribute

meson.build

@@ -549,6 +549,15 @@ foreach attr : possible_c_attributes
         conf.set10('HAVE_ATTRIBUTE_' + attr.to_upper(), have)
 endforeach
 
+# TODO: drop this manual check when meson learns about this attribute
+possible_c_attributes += ['no_reorder']
+
+have = cc.compiles(
+        '__attribute__((__no_reorder__)) int x;',
+        args : '-Werror=attributes',
+        name : '__attribute__((__no_reorder__))')
+conf.set10('HAVE_ATTRIBUTE_NO_REORDER', have)
+
 #####################################################################
 # compilation result tests
 

src/fundamental/macro-fundamental.h

@@ -116,6 +116,12 @@
 #  define _retain_
 #endif
 
+#if HAVE_ATTRIBUTE_NO_REORDER
+#  define _no_reorder_ __attribute__((__no_reorder__))
+#else
+#  define _no_reorder_
+#endif
+
 #if __GNUC__ >= 15
 #  define _nonnull_if_nonzero_(p, n) __attribute__((nonnull_if_nonzero(p, n)))
 #else

src/shared/options.h

@@ -25,6 +25,7 @@ typedef struct Option {
         _alignptr_                                                      \
         _used_                                                          \
         _retain_                                                        \
+        _no_reorder_                                                    \
         _variable_no_sanitize_address_                                  \
         static const Option CONCATENATE(option, counter) = {            \
                 .id = 0x100 + counter,                                  \

src/shared/verbs.h

@@ -26,6 +26,7 @@ typedef struct {
         _alignptr_                                                      \
         _used_                                                          \
         _retain_                                                        \
+        _no_reorder_                                                    \
         _variable_no_sanitize_address_                                  \
         static const Verb CONCATENATE(verb_data_, __COUNTER__) = {      \
                 .verb = v,                                              \