[fuchsia][testing] Disable test that relies on partial munmap()

Fuchsia's munmap() doesn't support unmapping part of a previously
created mapping (tracked in MG-215). Disable a test that relies on
this when building for Fuchsia.

Change-Id: I667c564929ed58d83da002655cefd6dc8e3be1fd
diff --git a/re2/testing/re2_test.cc b/re2/testing/re2_test.cc
index 5566812..01d9e42 100644
--- a/re2/testing/re2_test.cc
+++ b/re2/testing/re2_test.cc
@@ -735,6 +735,9 @@
 // the number being parsed.
 // This implementation requires mmap(2) et al. and thus cannot
 // be used unless they are available.
+// TODO(Fuchsia): This test fails on fuchsia due to munmap() of part of a region
+// not being supported, see MG-215
+#ifndef __Fuchsia__
 TEST(RE2, NULTerminated) {
 #if defined(_POSIX_MAPPED_FILES) && _POSIX_MAPPED_FILES > 0
   char *v;
@@ -756,6 +759,7 @@
   CHECK_EQ(x, 1);
 #endif
 }
+#endif  // __Fuchsia__
 
 TEST(RE2, FullMatchTypeTests) {
   // Type tests