[basic.start.main] Clarify meaning of "contain a function"

Author: lprv

source/basic.tex

@@ -7187,7 +7187,7 @@
 
 \pnum
 \indextext{program!startup|(}%
-A program shall contain exactly one function called \tcode{main}
+A program shall contain exactly one definition of a function called \tcode{main}
 that belongs to the global scope.
 Executing a program starts a main thread of execution\iref{intro.multithread,thread.threads}
 in which the \tcode{main} function is invoked.