[rt][nfc] Rewrite #ifndef as #if defined(). am: 2d999118b7

Original change: https://android-review.googlesource.com/c/platform/external/gwp_asan/+/1775247

Change-Id: Ib655e778a0f5748ede78dfba47d2aebb0c730120
diff --git a/gwp_asan/tests/backtrace.cpp b/gwp_asan/tests/backtrace.cpp
index 7a3427e..a4eb8eb 100644
--- a/gwp_asan/tests/backtrace.cpp
+++ b/gwp_asan/tests/backtrace.cpp
@@ -46,7 +46,7 @@
 }
 
 TEST_F(BacktraceGuardedPoolAllocatorDeathTest, UseAfterFree) {
-#ifdef __linux__ && __ARM_ARCH == 7
+#if defined(__linux__) && __ARM_ARCH == 7
   // Incomplete backtrace on Armv7 Linux
   GTEST_SKIP();
 #endif