This CL fixes an upcoming clang compiler warning (-Wparentheses).

BuildAsciiCharFlags uses ternary operator '?' together with bitwise
or '|'. Bitwise or '|' binds stronger than '?', so BuildAsciiCharsFlags
is basically: return check1(c) ? E1
                  : (0 | check2(c)) ? E2
                       : (0 | check3(c)) ? E3
                           : 0;
This CL fixes this.

Change-Id: I794ef4aa19786e61b23d1f2b35eff486cf6d569a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1738850Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Simon Zünd <szuend@chromium.org>
Commit-Queue: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63091}