Make the environment_variables test less flaky.

The test was inadvertently depending on the ordering of output between
stderr and stdout, which makes it break particularly when being run
remotely.

rdar://88335113

Author: al45tair

test/Runtime/environment_variables.swift

@@ -6,7 +6,8 @@
 // UNSUPPORTED: use_os_stdlib
 // UNSUPPORTED: back_deployment_runtime
 
-// RUN: env %env-SWIFT_DEBUG_HELP=YES %env-SWIFT_DEBUG_SOME_UNKNOWN_VARIABLE=42 %env-SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION=YES %env-SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=abc %env-SWIFT_DETERMINISTIC_HASHING=whatever %env-SWIFT_ENABLE_MANGLED_NAME_VERIFICATION=YES %env-SWIFT_DEBUG_ENABLE_MALLOC_SCRIBBLE=YES %target-run %t/main 2>&1 | %FileCheck %s --dump-input fail
+// RUN: env %env-SWIFT_DEBUG_HELP=YES %env-SWIFT_DEBUG_SOME_UNKNOWN_VARIABLE=42 %env-SWIFT_DEBUG_ENABLE_METADATA_ALLOCATION_ITERATION=YES %env-SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=abc %env-SWIFT_DETERMINISTIC_HASHING=whatever %env-SWIFT_ENABLE_MANGLED_NAME_VERIFICATION=YES %env-SWIFT_DEBUG_ENABLE_MALLOC_SCRIBBLE=YES %target-run %t/main >%t.out 2>%t.err
+// RUN: cat %t.err %t.out | %FileCheck %s --dump-input fail
 
 // CHECK-DAG: {{Warning: unknown environment variable SWIFT_DEBUG_SOME_UNKNOWN_VARIABLE|Using getenv to read variables. Unknown SWIFT_DEBUG_ variables will not be flagged.}}
 // CHECK-DAG: Warning: cannot parse value SWIFT_DEBUG_IMPLICIT_OBJC_ENTRYPOINT=abc, defaulting to 2.
@@ -18,5 +19,8 @@
 // CHECK-DAG:    bool SWIFT_ENABLE_MANGLED_NAME_VERIFICATION [default: false] - Enable verification that metadata can roundtrip through a mangled name each time metadata is instantiated.
 // CHECK-DAG:    bool SWIFT_DEBUG_ENABLE_MALLOC_SCRIBBLE [default: false] - Scribble on runtime allocations such as metadata allocations.
 
-print("Hello, world")
+// We need to do this because the DAG checks require a non-DAG check as an
+// anchor:
+
 // CHECK: Hello, world
+print("\nHello, world\n")