Split `targets` tool logic, moving all the compiler-specific flags to a
new `common_compiler_flags.py` file, and everything else (CPPDEFINES,
optimize option logic, dev build logic, etc) to the `godotcpp` tool.
The default tools now apply the common compiler flags by importing the
file and explicitly calling `configure`.
This comment enables the possibility to build the "compile_commands.json"
file by only using `scons -Q compiledb`. No need to use the argument
`compiledb=yes`.
And when using the `compiledb=yes`, it will create a
"compiled_commands.json" automatically.