Vulkan debugger: Don't wait for debugger by default.
Vulkan debugger: Don't wait for debugger by default.

Only wait when the `VK_WAIT_FOR_DEBUGGER` env var is set.
Long term I want to move away from relying on environment variables, but this is currently consistent with the `VK_DEBUGGER_PORT` env var which also enables the debugger.

Bug: b/148135662
Change-Id: I990d907d7570569e9d6716cf5d13e9846f4a5c02
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/40429
Reviewed-by: Antonio Maiorano <86d87a6550afb6b07035c9743fa181900589f7e0@google.com>
Tested-by: Ben Clayton <1f693eb7158dc33015048c09d6712f74dabddf79@google.com>
Kokoro-Presubmit: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader