Switch the rest of our internal headers to #pragma once.

We've been using #pragma once for new internal files, but let's be more bold.

Bug: N/A
Test: builds
Change-Id: I7e2ee2730043bd884f9571cdbd8b524043030c07
diff --git a/libm/fpmath.h b/libm/fpmath.h
index 80420e5..854ba11 100644
--- a/libm/fpmath.h
+++ b/libm/fpmath.h
@@ -33,8 +33,7 @@
 // - android uses 128 bits long doubles for LP64, so the structure and macros
 //   were reworked for the quad precision ieee representation.
 
-#ifndef _FPMATH_
-#define _FPMATH_
+#pragma once
 
 #include <endian.h>
 
@@ -92,5 +91,3 @@
 } while(0)
 
 #endif // __LP64__
-
-#endif // _FPMATH_
diff --git a/libm/freebsd-compat.h b/libm/freebsd-compat.h
index ee41e45..0bcc40d 100644
--- a/libm/freebsd-compat.h
+++ b/libm/freebsd-compat.h
@@ -14,8 +14,7 @@
  * limitations under the License.
  */
 
-#ifndef _BIONIC_LIBM_FREEBSD_COMPAT_H_included
-#define _BIONIC_LIBM_FREEBSD_COMPAT_H_included
+#pragma once
 
 #include <float.h>
 
@@ -38,5 +37,3 @@
 
 // Similarly rename _scan_nan.
 #define _scan_nan __libm_scan_nan
-
-#endif