headers: Remove useless HAVE_CONFIG_H macros

We do not have non-cmake build options, cmake always does configure_file.

CMakeLists.txt

@@ -275,7 +275,6 @@ else()
 endif()
 
 add_definitions(-DINCLUDE_GENERATED_DECLARATIONS)
-add_definitions(-DHAVE_CONFIG_H)
 
 if(CMAKE_COMPILER_IS_GNUCXX AND CMAKE_SYSTEM_NAME STREQUAL "Linux")
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -Wl,--no-undefined")

src/nvim/iconv.h

@@ -10,9 +10,7 @@
 // USE_ICONV, or to put the USE_ICONV definition in config.h.in directly. As
 // it stands, globals.h needs to be included alongside iconv.h.
 
-#ifdef HAVE_CONFIG_H
-# include "auto/config.h"
-#endif
+#include "auto/config.h"
 
 // Use iconv() when it's available, either by linking to the library at
 // compile time or by loading it at runtime.

src/nvim/vim.h

@@ -13,18 +13,16 @@
 
 /* ============ the header file puzzle (ca. 50-100 pieces) ========= */
 
-#ifdef HAVE_CONFIG_H    /* GNU autoconf (or something else) was here */
-# include "auto/config.h"
-# define HAVE_PATHDEF
+#include "auto/config.h"
+#define HAVE_PATHDEF
 
 /*
  * Check if configure correctly managed to find sizeof(int).  If this failed,
  * it becomes zero.  This is likely a problem of not being able to run the
  * test program.  Other items from configure may also be wrong then!
  */
-# if (SIZEOF_INT == 0)
-Error: configure did not run properly.Check auto/config.log.
-# endif
+#if (SIZEOF_INT == 0)
+# error Configure did not run properly.
 #endif
 
 #include "nvim/os/os_defs.h"       /* bring lots of system header files */