For

double data[20000000] = {0};

we would blow out the memory by creating 20M Exprs to fill out the initializer.

To fix this, if the initializer list initializes an array with more elements than
there are initializers in the list, have InitListExpr store a single 'ArrayFiller' expression
that specifies an expression to be used for value initialization of the rest of the elements.

Fixes rdar://9275920.

llvm-svn: 129896