Fix the incorrect detection of ICONV_LIBRARY_PATH

[skatkov]

Summary

This is introduced in rL308711.
Check for c library is incorrect here just because libc will be found always
and it does not mean that iconv is presented.

Thank to Andrew Krasny for narrowing down the root cause.

cmake/config-ix.cmake

foreach(library tinfo terminfo curses ncurses ncursesw)
         set(TERMINFO_LIBS "${library}")
         break()
       endif()
     endforeach()
   else()
     set(HAVE_TERMINFO 0)
   endif()
 
-  find_library(ICONV_LIBRARY_PATH NAMES iconv libiconv libiconv-2 c)
+  find_library(ICONV_LIBRARY_PATH NAMES iconv libiconv libiconv-2)
   set(LLVM_LIBXML2_ENABLED 0)
   set(LIBXML2_FOUND 0)
   if((LLVM_ENABLE_LIBXML2) AND (CMAKE_SYSTEM_NAME MATCHES "Linux") AND (ICONV_LIBRARY_PATH))
     find_package(LibXml2)
     if (LIBXML2_FOUND)
       set(LLVM_LIBXML2_ENABLED 1)
       include_directories(${LIBXML2_INCLUDE_DIR})
       set(LIBXML2_LIBS "xml2")