silence clang array bounds warnings

[zbigniew]

There is a data[ 1 ] declaration in C_block_struct, which is needed for a variable length structure in C89. However, in clang this produces a ton of warnings unless you silence them with -Wno-array-bounds.

Solution: if C99 mode is detected--the default in clang--use a flexible array member instead. This is the portable way to do it for C99 compilers, and as a benefit, shuts clang up.

If you don't have to clang to test, you can use gcc with --std=c99 or --std=gnu99 to activate the code path.