avutil: Fix linking x86 asm constants with Clang in MSVC mode

This fixes building with Clang in MSVC mode, for x86, which was
broken in 6e49b86 (in Nov 2024);
previously it failed with undefined symbols for the constants
defined with DECLARE_ASM_CONST, accessed via inline assembly.

Before 5786191, there was an
    #elif defined(__GNUC__) || defined(__clang__)
case before the
    #elif defined(_MSC_VER)
case for defining DECLARE_ASM_CONST, which included av_used.
(This case included the explicit "defined(__clang__)" since
f637046.)

After 5786191, it used the
generic definition of DECLARE_ASM_CONST that also included
av_used - which also worked for Clang in MSVC mode. But after
6e49b86, Clang in MSVC mode
ended up using the MSVC specific variant which lacked the
av_used declaration, causing linker errors due to undefined
symbols.

Signed-off-by: Martin Storsjö <martin@martin.st>

Author: mstorsjo

libavutil/mem_internal.h

@@ -82,8 +82,8 @@
     #define DECLARE_ASM_CONST(n,t,v)    alignas(FFMIN(n, 16)) static const t av_used v
 #elif defined(_MSC_VER)
     #define DECLARE_ALIGNED_T(n,t,v)    __declspec(align(n)) t v
-    #define DECLARE_ASM_ALIGNED(n,t,v)  __declspec(align(n)) t v
-    #define DECLARE_ASM_CONST(n,t,v)    __declspec(align(n)) static const t v
+    #define DECLARE_ASM_ALIGNED(n,t,v)  __declspec(align(n)) t av_used v
+    #define DECLARE_ASM_CONST(n,t,v)    __declspec(align(n)) static const t av_used v
 #else
     #define DECLARE_ALIGNED_T(n,t,v)    alignas(n) t v
     #define DECLARE_ASM_ALIGNED(n,t,v)  alignas(n) t av_used v