All that shows is that you have got a main() in the source files for
LogTest and no main() in the source files for WriteStr2File
Most likely that means you changed 'TOOL_NAME = LogTest' to 'TOOL_NAME
= WriteStr2File' but forgot to change 'LogTest_OBJC_FILES = source.m'
to 'WriteStr2File_OBJC_FILES = source.m'
In that case you are telling it to build the tool 'WriteStr2File', but
telling it that the source files list (WriteStr2File_OBJC_FILES) is
empty.
If there are no source files, then of course main() is not found in
any of the source files, so you get the linker error saying that.