Add note on GCC compiler flags

Add a note on GCC compiler flags

-A needs an assertion -B needs a argument -D needs a macro name (Defines a macro with the specified name) -F needs a path (Specifies a directory to search for header files) -I needs a path ( Adds a directory to the list of directories to be searched for header files during preprocessing ) -J needs an argument -L needs an argument (specifies the linking directory) (specify a directory to search for libraries during the linking phase) -R needs an argument -T needs an argument -U needs a macro name (This flag is used to undefine a macro) -d needs an argument -e needs an argument -g includes debug symbols -h needs an argument -l (lower case I) needs an argument -o needs a file name (specifies the output files) -l (lower case L) needs and argument (This flag is used to link against a specific library) -u needs an argument (used in symbol linking) -v is verbose? -x needs an argument (used to specify the language of the input files) -z needs an argument

Needs moar research.