Prevent appending "-g" after "-g3" to compile options in info-macros.exp.

Prevent appending "-g" after "-g3" to compile options in info-macros.exp.

When upstream gcc is given a command line with the "-g" option after
"-g3", it doesn't generate a ".debug_macro" section.  This is because
the last option wins, thus downgrading the debug level again.  Without
any macro debug information in the executable, info-macros.exp
obviously produces many failures.

Since the "-g" option is appended by DejaGnu's target_compile whenever
the "debug" option is set, the fix just removes that option.

gdb/testsuite/ChangeLog:
	* gdb.base/info-macros.exp: Remove "debug" from the compile
	options.