Isolate machine-dependent use of <alloca.h> in "Support/Alloca.h",

so that we can easily change its use to be conditional on the result of
an autoconf test later.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@6723 91177308-0d34-0410-b5e6-96231b3b80d8

include/Support/Alloca.h

@@ -0,0 +1,30 @@
+//===-- include/Support/Alloca.h - Support for alloca header -----*- C++ -*--=//
+//
+// Some platforms do not have alloca.h; others do. You can include this
+// file instead of <alloca.h> and it will include <alloca.h> on the platforms
+// that require you to do so to use alloca().
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_ALLOCA_H
+#define LLVM_SUPPORT_ALLOCA_H
+
+// TODO: Determine HAVE_ALLOCA_H based on autoconf results.
+// The following method is too brittle.
+#if defined(HAVE_ALLOCA_H)
+#undef HAVE_ALLOCA_H
+#endif
+
+#if defined(__linux__)
+#define HAVE_ALLOCA_H 1
+#elif defined(__sparc__)
+#define HAVE_ALLOCA_H 1
+#elif defined(__FreeBSD__)
+// not defined here
+#endif
+
+#if HAVE_ALLOCA_H
+#include <alloca.h>
+#endif
+
+#endif  /* LLVM_SUPPORT_ALLOCA_H */