[MemProf] Reenable test with fix for bot failures

[tejohnson]

Summary

The issue was unexpected macro expansion when the bot's test output
directory contained a token matching a build system macro (e.g.
"linux"). Switch to using a hardcoded path, which is invalid but is
sufficient for ensuring that the path is passed down to the runtime.

compiler-rt/test/memprof/TestCases/log_path_test.cpp

 // Invalid log_path.
 // RUN: %env_memprof_opts=log_path=/dev/null/INVALID not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-INVALID --dump-input=always
 
 // Too long log_path.
 // RUN: %env_memprof_opts=log_path=`for((i=0;i<10000;i++)); do echo -n $i; done` \
 // RUN:   not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-LONG --dump-input=always
 
 // Specifying the log name via the __memprof_profile_filename variable.
-// Temporarily disable until bot failures fixed
-// %clangxx_memprof  %s -o %t -DPROFILE_NAME_VAR="%t.log2"
-// rm -f %t.log2.*
-// %run %t
-// FileCheck %s --check-prefix=CHECK-GOOD --dump-input=always < %t.log2.*
+// Note we use an invalid path since that is sufficient for checking that the
+// specified __memprof_profile_filename value is passed through to the runtime.
+// Using an automatically generated name via %t can cause weird issues with
+// unexpected macro expansion if the path includes tokens that match a build
+// system macro (e.g. "linux").
+// RUN: %clangxx_memprof  %s -o %t -DPROFILE_NAME_VAR="/dev/null/INVALID"
+// RUN: not %run %t 2>&1 | FileCheck %s --check-prefix=CHECK-INVALID --dump-input=always
 
 #ifdef PROFILE_NAME_VAR
 #define xstr(s) str(s)
 #define str(s) #s
 char __memprof_profile_filename[] = xstr(PROFILE_NAME_VAR);
 #endif
 
 #include <stdlib.h>