Makefile: Disable constant merging/optimziations with clang

Clang optimizes static constant variables if both variables are
having same value. clang decided to merge the bpf_prog_iops and
bpf_map_iops into a single memory location, such that the two
i_ops could then not be distinguished anymore and leading to
kernel panic. So disable Snapdragon specific compiler optimizations
by adding -mllvm -disable-struct-const-merge flag to CFLAG.

Change-Id: I3a8d3829fd5102c916e74af4080a1b1d2d3257b9
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>