Automatic detection of the arm architecture does not work well.

http://downloads.lede-project.org/snapshots/faillogs/arm_arm1176jzf-s_vfp/packages/node/compile.txt

```
../deps/v8/src/arm/assembler-arm.cc:176:2: error: #error "CAN_USE_ARMV7_INSTRUCTIONS should match CAN_USE_VFP3_INSTRUCTIONS"
 #error "CAN_USE_ARMV7_INSTRUCTIONS should match CAN_USE_VFP3_INSTRUCTIONS"
   ^~~~~
```

https://github.com/openwrt/packages/issues/5728

Explicitly set cpu arch optimization flag to the compiler option so that "configure" script correctly identifies "arm version".

(Raspberry Pi Zero W)
Raspbian:
```
raspberrypi:~ $ echo | gcc -dM -E - | grep ARM_ARCH
```
OpenWrt (cross-env):
```
ubuntu:~ $ echo | ./arm-openwrt-linux-muslgnueabi-gcc -dM -E - | grep ARM_ARCH
```
```
ubuntu:~ $ echo | ./arm-openwrt-linux-muslgnueabi-gcc -mcpu=arm1176jzf-s -dM -E - | grep ARM_ARCH
```

Also specifying an option lines compactly.

Signed-off-by: Hirokazu MORIKAWA <morikw2@gmail.com>