[asan] Allow propagating env variables when testing on iOS Simulator

[kubamracek]

Summary

This patch adds %env as a way to express that the environment variable should be set on the target device/simulator. This fixes some test failures when testing on iOS/Simulator.

compiler-rt/trunk/test/asan/TestCases/Darwin/scribble.cc

 // RUN: %clang_asan -O2 %s -o %t
 // RUN: %run %t 2>&1 | FileCheck --check-prefix=CHECK-NOSCRIBBLE %s
-// RUN: env MallocScribble=1 MallocPreScribble=1 %run %t 2>&1 | FileCheck --check-prefix=CHECK-SCRIBBLE %s
+// RUN: %env MallocScribble=1 MallocPreScribble=1 %run %t 2>&1 | FileCheck --check-prefix=CHECK-SCRIBBLE %s
 // RUN: %env_asan_opts=max_free_fill_size=4096 %run %t 2>&1 | FileCheck --check-prefix=CHECK-SCRIBBLE %s
 
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
 struct Isa {

compiler-rt/trunk/test/lit.common.cfg

 # in RUN lines.
 config.substitutions.append(
     (' clang', """\n\n*** Do not use 'clangXXX' in tests,
      instead define '%clangXXX' substitution in lit config. ***\n\n""") )
 
 # Allow tests to be executed on a simulator or remotely.
 if config.emulator:
   config.substitutions.append( ('%run', config.emulator) )
+  config.substitutions.append( ('%env ', "env ") )
 elif config.ios:
   device_id_env = "SANITIZER_IOSSIM_TEST_DEVICE_IDENTIFIER" if config.iossim else "SANITIZER_IOS_TEST_DEVICE_IDENTIFIER"
   if device_id_env in os.environ: config.environment[device_id_env] = os.environ[device_id_env]
   ios_commands_dir = os.path.join(config.compiler_rt_src_root, "test", "sanitizer_common", "ios_commands")
   run_wrapper = os.path.join(ios_commands_dir, "iossim_run.py" if config.iossim else "ios_run.py")
   config.substitutions.append(('%run', run_wrapper))
+  env_wrapper = os.path.join(ios_commands_dir, "iossim_env.py" if config.iossim else "ios_env.py")
+  config.substitutions.append(('%env ', env_wrapper + " "))
 else:
   config.substitutions.append( ('%run', "") )
+  config.substitutions.append( ('%env ', "env ") )
 
 # Define CHECK-%os to check for OS-dependent output.
 config.substitutions.append( ('CHECK-%os', ("CHECK-" + config.host_os)))
 
 # Define %arch to check for architecture-dependent output.
 config.substitutions.append( ('%arch', (config.host_arch)))
 
 if config.host_os == 'Windows':