True by default, allows forcing non-optimized builds of SwiftShader in
debug builds.

Bug: b/140251624
Change-Id: I51bb93b53ead5936b47894ebabbd73b36c05cae0
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/36470Tested-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>