Bump __clang_minor__ check to 6 for __builtin_isnan

It appears that upstream 3.5 still can't accept __builtin_isnan redeclared
with calling convention, eg.

cat > isnan.c <<EOF
int __builtin_isnan(double) __attribute__((pcs("aapcs")));
EOF

  clang  -target armv5te-none-linux-androideabi -c isnan.c
  isnan.c:1:5: error: function declared 'aapcs' here was previously declared without calling convention
  int __builtin_isnan(double) __attribute__((pcs("aapcs")));
      ^
  isnan.c:1:5: note: previous declaration is here

Change-Id: Iff466fd913c3deec27aa3ff355a208543028d368
Merge "Bump __clang_minor__ check to 6 for __builtin_isnan"
auto-merger: merge in from aosp/master