Set HOME for tests that use module cache path

Getting the default module cache path calls llvm::sys::path::cache_directory,
which calls home_directory, which checks the HOME environment variable
before falling back to getpwuid.  When compiling against musl libc,
which does not support NSS, and running on a machine that doesn't have
the current user in /etc/passwd due to NSS, no home directory can
be found.  Set the HOME environment variable in the tests to avoid
depending on getpwuid.

Reviewed By: pirama, srhines

Differential Revision: https://reviews.llvm.org/D132984

clang/test/Driver/modules-cache-path.m

@@ -1,4 +1,4 @@
-// RUN: %clang -fmodules -### %s 2>&1 | FileCheck %s -check-prefix=CHECK-DEFAULT
+// RUN: env HOME=%t.home %clang -fmodules -### %s 2>&1 | FileCheck %s -check-prefix=CHECK-DEFAULT
 // CHECK-DEFAULT: -fmodules-cache-path={{.*}}clang{{[/\\]+}}ModuleCache
 
 // RUN: env CLANG_MODULE_CACHE_PATH=/dev/null \

clang/test/Modules/driver.c

@@ -1,4 +1,4 @@
-// RUN: %clang -fmodules -fimplicit-module-maps %s -### 2>&1 | FileCheck -check-prefix CHECK-NO_MODULE_CACHE %s
+// RUN: env HOME=%t.home %clang -fmodules -fimplicit-module-maps %s -### 2>&1 | FileCheck -check-prefix CHECK-NO_MODULE_CACHE %s
 // RUN: %clang -fmodules -fimplicit-module-maps -fmodules-cache-path=blarg %s -### 2>&1 | FileCheck -check-prefix CHECK-WITH_MODULE_CACHE %s
 
 // CHECK-NO_MODULE_CACHE: {{clang.*"-fmodules-cache-path=.*ModuleCache"}}

clang/test/Unit/lit.cfg.py

@@ -30,6 +30,9 @@ if 'TMP' in os.environ:
 if 'TEMP' in os.environ:
     config.environment['TEMP'] = os.environ['TEMP']
 
+if 'HOME' in os.environ:
+    config.environment['HOME'] = os.environ['HOME']
+
 # Propagate sanitizer options.
 for var in [
     'ASAN_SYMBOLIZER_PATH',