build-thirdparty.sh has bad gcc link

[0xSSoul]

Describe the bug
build-thirdparty.sh assume gcc is in /bin/gcc if there is no palo-toolchain/gcc. But, in many Linux distribution gcc is in /usr/bin/gcc. Actually, if default gcc is used, use "gcc" directly from PATH.

To Reproduce
Steps to reproduce the behavior:

1. build-thirdparty.sh
2. See error
   ./build-thirdparty.sh: line 114: /bin/gcc: No such file or directory

Expected behavior

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu
• Version: 16.04

Additional context
After fix #231

[0xSSoul]

commit： ae19fbf has fixed all the issues.

[0xSSoul]

commit： ae19fbf has fixed all the issues.