[Remote Test] Fix remote-run to process environment variables.

`remote-run` should look in the environment for input/output paths as
well as considering command line arguments.

With this change, `test/Runtime/Paths.cpp` should work for remote testing
and device testing.

rdar://106294557

Author: al45tair

test/Runtime/Paths.cpp

@@ -10,7 +10,6 @@
 // RUN: %target-run %t/paths-test | %FileCheck %s
 // RUN: env %env-SWIFT_ROOT=%t/swift-root %target-run %t/paths-test | %FileCheck %s --check-prefix CHECK-FR
 // REQUIRES: executable_test
-// UNSUPPORTED: remote_run
 
 // This can't be done in unittests, because that statically links the runtime
 // so we get the wrong paths.  We explicitly want to test that we get the

test/remote-run/Inputs/upload/3.txt

@@ -1,10 +1,10 @@
 REQUIRES: sftp_server
 
-RUN: %debug-remote-run --input-prefix %S/Inputs/upload/ ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE %s
+RUN: env REMOTE_RUN_CHILD_FOO=%S/Inputs/upload/3.txt %debug-remote-run --input-prefix %S/Inputs/upload/ ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE %s
 RUN: ls %t-REMOTE/input/ | %FileCheck %s
 
 RUN: %empty-directory(%t-REMOTE)
-RUN: %debug-remote-run --input-prefix %S/Inputs/ ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE-NESTED %s
+RUN: env REMOTE_RUN_CHILD_FOO=%S/Inputs/upload/3.txt %debug-remote-run --input-prefix %S/Inputs/ ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE-NESTED %s
 RUN: ls %t-REMOTE/input/upload/ | %FileCheck %s
 RUN: %debug-remote-run -v --input-prefix %S/Inputs/ ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt 2>&1 >/dev/null | %FileCheck -check-prefix VERBOSE-NESTED %s
 
@@ -13,7 +13,7 @@ RUN: %debug-remote-run --input-prefix %S/Inputs/upload/1 ls %S/Inputs/upload/1.t
 RUN: test -f %t-REMOTE/input/1.txt
 
 RUN: %empty-directory(%t-REMOTE)
-RUN: %debug-remote-run --input-prefix %S/Inputs/upload/ --remote-input-prefix custom-input ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE-CUSTOM %s
+RUN: env REMOTE_RUN_CHILD_FOO=%S/Inputs/upload/3.txt %debug-remote-run --input-prefix %S/Inputs/upload/ --remote-input-prefix custom-input ls %S/Inputs/upload/1.txt %S/Inputs/upload/2.txt | %FileCheck -check-prefix CHECK-REMOTE-CUSTOM %s
 RUN: ls %t-REMOTE/custom-input/ | %FileCheck %s
 
 CHECK-REMOTE: {{-REMOTE/input/1.txt$}}
@@ -30,6 +30,7 @@ CHECK-REMOTE-CUSTOM-NEXT: {{-REMOTE/custom-input/2.txt$}}
 CHECK-NOT: BAD
 CHECK: {{^1.txt$}}
 CHECK-NEXT: {{^2.txt$}}
+CHECK-NEXT: {{^3.txt$}}
 CHECK-NOT: BAD
 
 VERBOSE-NESTED: /usr/bin/env /bin/mkdir -p {{.+}}-REMOTE/input