tree-wide: use '#pragma once' for header guard

Follow-up for a2b635eb39 (#9959).

src/basic/MurmurHash2.h

@@ -2,8 +2,7 @@
 // MurmurHash2 was written by Austin Appleby, and is placed in the public
 // domain. The author hereby disclaims copyright to this source code.
 
-#ifndef _MURMURHASH2_H_
-#define _MURMURHASH2_H_
+#pragma once
 
 //-----------------------------------------------------------------------------
 // Platform-specific functions and macros
@@ -29,5 +28,3 @@ typedef unsigned __int64 uint64_t;
 uint32_t MurmurHash2        ( const void * key, int len, uint32_t seed );
 
 //-----------------------------------------------------------------------------
-
-#endif // _MURMURHASH2_H_

src/basic/securebits.h

@@ -1,5 +1,4 @@
-#ifndef _LINUX_SECUREBITS_H
-#define _LINUX_SECUREBITS_H 1
+#pragma once
 
 /* This is minimal version of Linux' linux/securebits.h header file,
  * which is licensed GPL2 */
@@ -41,5 +40,3 @@
                                  issecure_mask(SECURE_NO_SETUID_FIXUP) | \
                                  issecure_mask(SECURE_KEEP_CAPS))
 #define SECURE_ALL_LOCKS	(SECURE_ALL_BITS << 1)
-
-#endif /* !_LINUX_SECUREBITS_H */

src/basic/sparse-endian.h

@@ -20,8 +20,7 @@
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
  * IN THE SOFTWARE.
  */
-#ifndef SPARSE_ENDIAN_H
-#define SPARSE_ENDIAN_H
+#pragma once
 
 #include <byteswap.h>
 #include <endian.h>
@@ -89,5 +88,3 @@ static inline uint64_t be64toh(be64_t value) { return bswap_64_on_le((uint64_t _
 
 #undef __sd_bitwise
 #undef __sd_force
-
-#endif /* SPARSE_ENDIAN_H */