libbpf: Hashmap.h update to fix build issues using LLVM14

A fix for the LLVM compilation error while building bpftool.
Replaces the expression:

_Static_assert((p) == NULL || ...)

by expression:

_Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) || ...)

When "p" is not a constant the former is not considered to be a
constant expression by LLVM 14.

The error was introduced in the following patch-set: [1].
The error was reported here: [2].

[1] https://lore.kernel.org/bpf/[e-mail]/
[2] https://lore.kernel.org/all/[e-mail]/

Reported-by: kernel test robot <[e-mail]>
Fixes: c302378bc157 ("libbpf: Hashmap interface update to allow both long and void* keys/values")
Signed-off-by: Eduard Zingerman <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Stanislav Fomichev <[e-mail]>
Link: https://lore.kernel.org/bpf/[e-mail]

tools/lib/bpf/hashmap.h

···
 };
 
 #define hashmap_cast_ptr(p) ({								\
-	_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),			\
+	_Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) ||			\
+				sizeof(*(p)) == sizeof(long),				\
 		       #p " pointee should be a long-sized integer or a pointer");	\
 	(long *)(p);									\
 })

tools/perf/util/hashmap.h

···
 };
 
 #define hashmap_cast_ptr(p) ({								\
-	_Static_assert((p) == NULL || sizeof(*(p)) == sizeof(long),			\
+	_Static_assert((__builtin_constant_p((p)) ? (p) == NULL : 0) ||			\
+				sizeof(*(p)) == sizeof(long),				\
 		       #p " pointee should be a long-sized integer or a pointer");	\
 	(long *)(p);									\
 })