Make the host endianness check an integer constant expression.

I will remove the isBigEndianHost function once I update clang.

The ifdef logic is designed to
* not use configure/cmake to avoid breaking -arch i686 -arch ppc.
* default to little endian
* be as small as possible

It looks like sys/endian.h is the preferred header on most modern BSD systems,
but it is better to change this in a followup patch as machine/endian.h is
available on FreeBSD, OpenBSD, NetBSD and OS X.

llvm-svn: 179527
diff --git a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
index f100994..555ea96 100644
--- a/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
+++ b/llvm/lib/ExecutionEngine/RuntimeDyld/RuntimeDyldImpl.h
@@ -202,14 +202,14 @@
 
 
   void writeInt16BE(uint8_t *Addr, uint16_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 8) & 0xFF;
     *(Addr+1) = Value & 0xFF;
   }
 
   void writeInt32BE(uint8_t *Addr, uint32_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 24) & 0xFF;
     *(Addr+1) = (Value >> 16) & 0xFF;
@@ -218,7 +218,7 @@
   }
 
   void writeInt64BE(uint8_t *Addr, uint64_t Value) {
-    if (sys::isLittleEndianHost())
+    if (sys::IsLittleEndianHost)
       Value = sys::SwapByteOrder(Value);
     *Addr     = (Value >> 56) & 0xFF;
     *(Addr+1) = (Value >> 48) & 0xFF;