[libFuzzer] Fix -Wunused-variable when building with NDEBUG (#188301)

The variable `FuzzerInitIsRunning` is only used within `assert()`.
Follow up to #178342.

GitOrigin-RevId: 9fd8bc0f0eedd3d6ca2c71f90de768a7759ab44c

FuzzerInterceptors.cpp

diff --git a/FuzzerInterceptors.cpp b/FuzzerInterceptors.cpp
index d5b0a42..3960dc0 100644
--- a/FuzzerInterceptors.cpp
+++ b/FuzzerInterceptors.cpp
@@ -48,7 +48,9 @@
 }
 
 static int FuzzerInited = 0;
+#ifndef NDEBUG
 static bool FuzzerInitIsRunning;
+#endif
 
 static void fuzzerInit();
 
@@ -226,7 +228,9 @@
   assert(!FuzzerInitIsRunning);
   if (FuzzerInited)
     return;
+#ifndef NDEBUG
   FuzzerInitIsRunning = true;
+#endif
 
   REAL(bcmp) = reinterpret_cast<memcmp_type>(
       getFuncAddr("bcmp", reinterpret_cast<uintptr_t>(&bcmp)));
@@ -247,7 +251,9 @@
   REAL(memmem) = reinterpret_cast<memmem_type>(
       getFuncAddr("memmem", reinterpret_cast<uintptr_t>(&memmem)));
 
+#ifndef NDEBUG
   FuzzerInitIsRunning = false;
+#endif
   FuzzerInited = 1;
 }