Fix math functions optimization

replace fast-math with fp-contract=fast

Issue:#I66OCS
Test:xts test passed
Signed-off-by: Nguzhihao4 <guzhihao4@huawei.com>
Change-Id: Id565e00a3285cf3753818122a9862ac87c46e793

musl_template.gni

@@ -596,7 +596,7 @@ template("musl_libs") {
     cflags = [
       "-mllvm",
       "-instcombine-max-iterations=0",
-      "-ffast-math",
+      "-ffp-contract=fast",
       "-O3",
       "-fPIC",
       "-fstack-protector-strong",