[compiler-rt][UBSan] Add env prefixes in test

This was another test that was not using an env prefix when setting an
environment variable. This was caught by the Sparc Solaris builder as it
is disabled by default on Linux.

https://lab.llvm.org/buildbot/#/builders/13/builds/10414

Author: boomanaiden154

compiler-rt/test/ubsan/TestCases/Misc/Posix/print_stack_trace.cpp

@@ -1,5 +1,5 @@
-// RUN: %clangxx -fsanitize=undefined -O0 %s -o %t && UBSAN_OPTIONS=stack_trace_format=DEFAULT:fast_unwind_on_fatal=1 %run %t 2>&1 | FileCheck %s
-// RUN: %clangxx -fsanitize=undefined -O0 %s -o %t && UBSAN_OPTIONS=stack_trace_format=DEFAULT:fast_unwind_on_fatal=0 %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx -fsanitize=undefined -O0 %s -o %t && env UBSAN_OPTIONS=stack_trace_format=DEFAULT:fast_unwind_on_fatal=1 %run %t 2>&1 | FileCheck %s
+// RUN: %clangxx -fsanitize=undefined -O0 %s -o %t && env UBSAN_OPTIONS=stack_trace_format=DEFAULT:fast_unwind_on_fatal=0 %run %t 2>&1 | FileCheck %s
 
 // This test is temporarily disabled due to broken unwinding on ARM.
 // UNSUPPORTED: target={{.*-linux-.*}}