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 <amaiorano@google.com>
Tested-by: Ben Clayton <bclayton@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>

src/Vulkan/Debug/Server.cpp

diff --git a/src/Vulkan/Debug/Server.cpp b/src/Vulkan/Debug/Server.cpp
index d6e17b6..d283aa9 100644
--- a/src/Vulkan/Debug/Server.cpp
+++ b/src/Vulkan/Debug/Server.cpp
@@ -468,13 +468,18 @@
 		return dap::ConfigurationDoneResponse();
 	});
 
-	printf("Waiting for debugger connection...\n");
 	server->start(port, [&](const std::shared_ptr<dap::ReaderWriter> &rw) {
 		session->bind(rw);
 		ctx->addListener(this);
 	});
-	configurationDone.wait();
-	printf("Debugger connection established\n");
+
+	static bool waitForDebugger = getenv("VK_WAIT_FOR_DEBUGGER") != nullptr;
+	if(waitForDebugger)
+	{
+		printf("Waiting for debugger connection...\n");
+		configurationDone.wait();
+		printf("Debugger connection established\n");
+	}
 }
 
 Server::Impl::~Impl()