Don't inject matchpathcon_filespec_add64() ifdef __x86_64__

As the code notes, it wants to add an
  /* ABI backwards-compatible shim for non-LFS 32-bit systems */
it tries to detect these with
  #if defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64 && __BITS_PER_LONG < 64
which is correct with the added precondition that the ino_t /without/
-D_FILE_OFFSET_BITS=64 /was actually/ u32
(i.e. it conflates /all/ ILP32 systems into being non-LFS).

This is not the case on x32, for example, which is LFS; thus, the
  static_assert(sizeof(unsigned long) == sizeof(__ino_t), "inode size mismatch");
assertion fails (__ino_t is the "kernel ino_t" type,
which generally corresponds to the kernel's ulong, which is u64 on x32).

The correct spelling of the test for this is
  #if (...) && sizeof(__ino_t) == 4
but this is not statically solvable with the preprocessor.

Thus, we need to explcitly special-case this.
__x86_64__ indicates one of two ABIs (LP64 (amd64) or ILP32 (x32)),
both of which have ino_t=u64, and is the macro used for defining
__INO_T_TYPE in the system headers, so it's the best fit here.

Fixes: commit 9395cc0 ("Always build for LFS mode on 32-bit archs.")
Closes: #463
Closes: Debian#1098481

Author: nabijaczleweli

libselinux/include/selinux/selinux.h

@@ -537,7 +537,7 @@ extern int matchpathcon_index(const char *path,
    with the same inode (e.g. due to multiple hard links).  If so, then
    use the latter of the two specifications based on their order in the 
    file contexts configuration.  Return the used specification index. */
-#if defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64 && __BITS_PER_LONG < 64
+#if defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64 && __BITS_PER_LONG < 64 && !defined(__x86_64__)
 #define matchpathcon_filespec_add matchpathcon_filespec_add64
 #endif
 extern int matchpathcon_filespec_add(ino_t ino, int specind, const char *file);

libselinux/src/matchpathcon.c

@@ -261,7 +261,7 @@ int matchpathcon_filespec_add(ino_t ino, int specind, const char *file)
 	return -1;
 }
 
-#if defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64 && __BITS_PER_LONG < 64
+#if defined(_FILE_OFFSET_BITS) && _FILE_OFFSET_BITS == 64 && __BITS_PER_LONG < 64 && !defined(__x86_64__)
 /* alias defined in the public header but we undefine it here */
 #undef matchpathcon_filespec_add
 
@@ -282,7 +282,7 @@ int matchpathcon_filespec_add(unsigned long ino, int specind,
 }
 #else
 
-static_assert(sizeof(unsigned long) == sizeof(ino_t), "inode size mismatch");
+static_assert(sizeof(uint64_t) == sizeof(ino_t), "inode size mismatch");
 
 #endif