build: silence GCC warning on Linux

LLDWrapPython.cpp is a generated file.  This contains a double assignment to the
same value, which causes GCC to emit a warning about sequence point evaluation
causing a use-before-init.  Simply silence the warning.

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@213575 91177308-0d34-0410-b5e6-96231b3b80d8