Small typo in iconv.m4

[Nick Clifton]

Hi Hafiz,

> Hi All,
> Attached config/ patch was approved and committed in gcc repo. Ok to
> commit it in the binutils-gdb repo?
> 
> 2018-11-09  Hafiz Abid Qadeer  <abidh@codesourcery.com>
> 
> 	* config/iconv.m4 (AM_ICONV_LINK): Don't overwrite CPPFLAGS.
> 	Append $INCICONV to it.
> 	* gdb/configure: Regenerate.
> 	* binutils/configure: Likewise.
> 	* intl/configure: Likewise.

Approved, please apply.  I should note however that the changelog
entry probably should be split up and added to the respective
subdirectories ChangeLog files.  In particular I was confused because
I could not find a mention on the change in gcc's config/ChangeLog
file, and was rather surprised when I found it in the top level 
ChangeLog file instead.

Cheers
  Nick