Remove FORTIFY_SOURCE option for libc build

Issue:#I7JQOS

Test: pass libc-test and startup test
Signed-off-by: Nhaotuo <haotuo@huawei.com>
Change-Id: I4d5720ced892f7a1aa20870317d12fb01d043aab

musl_template.gni

@@ -103,7 +103,6 @@ template("musl_libs") {
     cflags_basic = [
       "--target=${musl_target_triple}",
       "-Wall",
-      "-D_FORTIFY_SOURCE=2",
       "-Wl,-z,relro,-z,now,-z,noexecstack",
     ]