Add change gcc options via Enviroment arguments.

[t2-kob]

I deleted Branch by mistake, so I will make a pull request again. Sorry!

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When acquiring benchmarks in multiple environments with different CPU architectures, The optimal gcc options differ from one environment to another.

For example, not all CPU architectures support "-march" or "-march=native".

These options are...

• Supported : x86, x86_64, ARM, AARCH64, etc..
• Not Supported: RISC-V, IBM Power, etc... (Check https://gcc.gnu.org/onlinedocs/gcc/Submodel-Options.html)

Therefore, by using the environment variable "UB_GCC_OPTIONS", gcc option can be externally changed.

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usage:

export UB_GCC_OPTIONS="-O3 -ffast-math -mcpu=power7"
./Run -i 1 -c 1 int