Modify tests to use executable memory.

The check_unreadble_elf_* tests only create a readable map. I changed
libunwind to disallow unwinding through non-executable maps, so make
the maps executable too.

Bug: 26589772
Change-Id: Idbe6426ac4d3243779b819c8f1aebdcdacb0669f
diff --git a/libbacktrace/backtrace_test.cpp b/libbacktrace/backtrace_test.cpp
index 23636db..7d829fe 100644
--- a/libbacktrace/backtrace_test.cpp
+++ b/libbacktrace/backtrace_test.cpp
@@ -1156,7 +1156,7 @@
   int fd = open(tmp_so_name, O_RDONLY);
   ASSERT_TRUE(fd != -1);
 
-  void* map = mmap(NULL, map_size, PROT_READ, MAP_PRIVATE, fd, 0);
+  void* map = mmap(NULL, map_size, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0);
   ASSERT_TRUE(map != MAP_FAILED);
   close(fd);
   ASSERT_TRUE(unlink(tmp_so_name) != -1);
@@ -1206,7 +1206,7 @@
       exit(0);
     }
 
-    void* map = mmap(NULL, map_size, PROT_READ, MAP_PRIVATE, fd, 0);
+    void* map = mmap(NULL, map_size, PROT_READ | PROT_EXEC, MAP_PRIVATE, fd, 0);
     if (map == MAP_FAILED) {
       fprintf(stderr, "Failed to map in memory: %s\n", strerror(errno));
       unlink(tmp_so_name);