Add AIX support to Path.inc, Host.h, and CMake.

Patch by Andrew Paprocki!

Differential Revision: https://reviews.llvm.org/D18359

llvm-svn: 276045
diff --git a/llvm/lib/Support/Unix/Path.inc b/llvm/lib/Support/Unix/Path.inc
index ea439c6..a01924c 100644
--- a/llvm/lib/Support/Unix/Path.inc
+++ b/llvm/lib/Support/Unix/Path.inc
@@ -90,7 +90,8 @@
 namespace fs {
 #if defined(__FreeBSD__) || defined (__NetBSD__) || defined(__Bitrig__) || \
     defined(__OpenBSD__) || defined(__minix) || defined(__FreeBSD_kernel__) || \
-    defined(__linux__) || defined(__CYGWIN__) || defined(__DragonFly__)
+    defined(__linux__) || defined(__CYGWIN__) || defined(__DragonFly__) || \
+    defined(_AIX)
 static int
 test_dir(char ret[PATH_MAX], const char *dir, const char *bin)
 {
@@ -161,7 +162,7 @@
   }
 #elif defined(__FreeBSD__) || defined (__NetBSD__) || defined(__Bitrig__) || \
       defined(__OpenBSD__) || defined(__minix) || defined(__DragonFly__) || \
-      defined(__FreeBSD_kernel__)
+      defined(__FreeBSD_kernel__) || defined(_AIX)
   char exe_path[PATH_MAX];
 
   if (getprogpath(exe_path, argv0) != NULL)