Remove incorrect uses of __attribute__((__malloc__)).

xrealloc() is obviously incorrect, modern GCC docs even
mention realloc() as an example where this attribute
cannot be used.

liblzma's lzma_alloc() and lzma_alloc_zero() would be
correct uses most of the time but custom allocators
may use a memory pool or otherwise hold the pointer
so aliasing issues could happen in theory.

The xstrdup() case likely was correct but I removed it anyway.
Now there are no __malloc__ attributes left in the code.
The allocations aren't in hot paths so this should make
no practical difference.

(cherry picked from commit 359e5c6cb1)

src/liblzma/common/common.c

@@ -35,7 +35,7 @@ lzma_version_string(void)
 // Memory allocation //
 ///////////////////////
 
-extern void * lzma_attribute((__malloc__)) lzma_attr_alloc_size(1)
+extern void * lzma_attr_alloc_size(1)
 lzma_alloc(size_t size, const lzma_allocator *allocator)
 {
 	// Some malloc() variants return NULL if called with size == 0.
@@ -53,7 +53,7 @@ lzma_alloc(size_t size, const lzma_allocator *allocator)
 }
 
 
-extern void * lzma_attribute((__malloc__)) lzma_attr_alloc_size(1)
+extern void * lzma_attr_alloc_size(1)
 lzma_alloc_zero(size_t size, const lzma_allocator *allocator)
 {
 	// Some calloc() variants return NULL if called with size == 0.

src/liblzma/common/common.h

@@ -280,12 +280,12 @@ struct lzma_internal_s {
 
 /// Allocates memory
 extern void *lzma_alloc(size_t size, const lzma_allocator *allocator)
-		lzma_attribute((__malloc__)) lzma_attr_alloc_size(1);
+		lzma_attr_alloc_size(1);
 
 /// Allocates memory and zeroes it (like calloc()). This can be faster
 /// than lzma_alloc() + memzero() while being backward compatible with
 /// custom allocators.
-extern void * lzma_attribute((__malloc__)) lzma_attr_alloc_size(1)
+extern void * lzma_attr_alloc_size(1)
 		lzma_alloc_zero(size_t size, const lzma_allocator *allocator);
 
 /// Frees memory

src/xz/util.h

@@ -20,11 +20,11 @@
 
 /// \brief      Safe realloc() that never returns NULL
 extern void *xrealloc(void *ptr, size_t size)
-		lzma_attribute((__malloc__)) lzma_attr_alloc_size(2);
+		lzma_attr_alloc_size(2);
 
 
 /// \brief      Safe strdup() that never returns NULL
-extern char *xstrdup(const char *src) lzma_attribute((__malloc__));
+extern char *xstrdup(const char *src);
 
 
 /// \brief      Fancy version of strtoull()