Fix PR6910.

Limit alignment in SmallVector 8, otherwise GCC assumes 16 byte alignment.
opetaror new, and malloc only return 8-byte aligned memory on 32-bit Linux,
which cause a crash if code is compiled with -O3 (or -ftree-vectorize) and some
SmallVector code is vectorized.

llvm-svn: 102604

llvm/include/llvm/ADT/SmallVector.h

@@ -59,7 +59,7 @@ protected:
   // number of union instances for the space, which guarantee maximal alignment.
   struct U {
 #ifdef __GNUC__
-    char X __attribute__((aligned));
+    char X __attribute__((aligned(8)));
 #else
     union {
       double D;