[using.linkage] Fix reference to C standard section.

Author: Stefanus Du Toit

source/lib-intro.tex

@@ -1231,7 +1231,7 @@
 \tcode{extern "C++"}
 linkage for this purpose.\footnote{The only reliable way to declare an object or
 function signature from the Standard C library is by including the header that
-declares it, notwithstanding the latitude granted in 7.1.7 of the C
+declares it, notwithstanding the latitude granted in 7.1.4 of the C
 Standard.}
 
 \pnum