cpp: Use #pragma once instead of #ifndef guards

This both says what we mean and silences a bunch of spurious CPP linting
warnings. This pragma is supported by all CPP implementations which we
support.

Reviewers: austin, erikd, simonmar, hvr

Reviewed By: simonmar

Subscribers: rwbarton, thomie

Differential Revision: https://phabricator.haskell.org/D3482

3 files changed, 3 insertions, 16 deletions

diff --git a/compiler/HsVersions.h b/compiler/HsVersions.h
index 4a0b04ad70..a4ec3e4c40 100644
--- a/compiler/HsVersions.h
+++ b/compiler/HsVersions.h
@@ -1,5 +1,4 @@
-#ifndef HSVERSIONS_H
-#define HSVERSIONS_H
+#pragma once
 
 #if 0
 
@@ -64,6 +63,3 @@ foreign import ccall unsafe saccessor                          \
 #define ASSERTM(e)      do { bool <- e; MASSERT(bool) }
 #define ASSERTM2(e,msg) do { bool <- e; MASSERT2(bool,msg) }
 #define WARNM2(e,msg)   do { bool <- e; WARN(bool, msg) return () }
-
-#endif /* HsVersions.h */
-
diff --git a/compiler/nativeGen/NCG.h b/compiler/nativeGen/NCG.h
index bca1de41e3..e7e20768b6 100644
--- a/compiler/nativeGen/NCG.h
+++ b/compiler/nativeGen/NCG.h
@@ -6,9 +6,6 @@
 
    -------------------------------------------------------------------------- */
 
-#ifndef NCG_H
-#define NCG_H
+#pragma once
 
 #include "ghc_boot_platform.h"
-
-#endif
diff --git a/compiler/utils/md5.h b/compiler/utils/md5.h
index 10c8dabd43..0b31f9019c 100644
--- a/compiler/utils/md5.h
+++ b/compiler/utils/md5.h
@@ -1,6 +1,5 @@
 /* MD5 message digest */
-#ifndef _MD5_H
-#define _MD5_H
+#pragma once
 
 #include "HsFFI.h"
 
@@ -17,8 +16,3 @@ void MD5Init(struct MD5Context *context);
 void MD5Update(struct MD5Context *context, byte const *buf, int len);
 void MD5Final(byte digest[16], struct MD5Context *context);
 void MD5Transform(word32 buf[4], word32 const in[16]);
-
-#endif /* _MD5_H */
-
-
-