build: don't define FUNC_ATTR_* as empty in headers (#26317)

FUNC_ATTR_* should only be used in .c files with generated headers.
Defining FUNC_ATTR_* as empty in headers causes misuses of them to be
silently ignored. Instead don't define them by default, and only define
them as empty after a .c file has included its generated header.

136 files changed, 142 insertions, 186 deletions

diff --git a/runtime/doc/dev_style.txt b/runtime/doc/dev_style.txt
index cb28f1a845..02fd07ce24 100644
--- a/runtime/doc/dev_style.txt
+++ b/runtime/doc/dev_style.txt
@@ -190,7 +190,7 @@ Function declarations ~
 
 Every function must not have a separate declaration.
 
-Function declarations are created by the gendeclarations.lua script. >c
+Function declarations are created by the gen_declarations.lua script. >c
 
     static void f(void);
 
diff --git a/src/klib/kvec.h b/src/klib/kvec.h
index 5677a93b1b..f9ecca3d55 100644
--- a/src/klib/kvec.h
+++ b/src/klib/kvec.h
@@ -160,10 +160,12 @@
    (v).size = 0, \
    (v).items = (v).init_array)
 
+static inline void *_memcpy_free(void *restrict dest, void *restrict src, size_t size)
+  REAL_FATTR_NONNULL_ALL REAL_FATTR_NONNULL_RET REAL_FATTR_ALWAYS_INLINE;
+
 /// Move data to a new destination and free source
 static inline void *_memcpy_free(void *const restrict dest, void *const restrict src,
                                  const size_t size)
-  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_NONNULL_RET FUNC_ATTR_ALWAYS_INLINE
 {
   memcpy(dest, src, size);
   XFREE_CLEAR(src);
diff --git a/src/nvim/CMakeLists.txt b/src/nvim/CMakeLists.txt
index 3505f8be4f..a8ce9edff8 100644
--- a/src/nvim/CMakeLists.txt
+++ b/src/nvim/CMakeLists.txt
@@ -463,7 +463,7 @@ endif()
 #-------------------------------------------------------------------------------
 
 get_target_property(prop main_lib INTERFACE_COMPILE_DEFINITIONS)
-foreach(gen_cdef DO_NOT_DEFINE_EMPTY_ATTRIBUTES ${prop})
+foreach(gen_cdef ${prop})
   if(NOT ${gen_cdef} MATCHES "INCLUDE_GENERATED_DECLARATIONS")
     list(APPEND gen_cflags "-D${gen_cdef}")
   endif()
diff --git a/src/nvim/api/autocmd.c b/src/nvim/api/autocmd.c
index 08d9d8e117..2ce08bdf40 100644
--- a/src/nvim/api/autocmd.c
+++ b/src/nvim/api/autocmd.c
@@ -17,7 +17,6 @@
 #include "nvim/buffer.h"
 #include "nvim/eval/typval.h"
 #include "nvim/ex_cmds_d