Simplify configure test

The test for lz4.h used AC_CHECK_HEADERS, but nothing was using the
resulting symbol HAVE_LZ4_H.  Change this to use AC_CHECK_HEADER
instead.  This was probably an oversight, seeing that the nearby
similar tests do this correctly.

configure

@@ -14103,19 +14103,13 @@ $as_echo "$LZ4" >&6; }
 fi
 
 if test "$with_lz4" = yes; then
-  for ac_header in lz4.h
-do :
   ac_fn_c_check_header_mongrel "$LINENO" "lz4.h" "ac_cv_header_lz4_h" "$ac_includes_default"
 if test "x$ac_cv_header_lz4_h" = xyes; then :
-  cat >>confdefs.h <<_ACEOF
-#define HAVE_LZ4_H 1
-_ACEOF
 
 else
   as_fn_error $? "lz4.h header file is required for LZ4" "$LINENO" 5
 fi
 
-done
 
 fi
 

configure.ac

@@ -1525,7 +1525,7 @@ fi
 
 PGAC_PATH_PROGS(LZ4, lz4)
 if test "$with_lz4" = yes; then
-  AC_CHECK_HEADERS(lz4.h, [], [AC_MSG_ERROR([lz4.h header file is required for LZ4])])
+  AC_CHECK_HEADER(lz4.h, [], [AC_MSG_ERROR([lz4.h header file is required for LZ4])])
 fi
 
 PGAC_PATH_PROGS(ZSTD, zstd)

src/include/pg_config.h.in

@@ -373,9 +373,6 @@
 /* Define to 1 if `long long int' works and is 64 bits. */
 #undef HAVE_LONG_LONG_INT_64
 
-/* Define to 1 if you have the <lz4.h> header file. */
-#undef HAVE_LZ4_H
-
 /* Define to 1 if you have the <mbarrier.h> header file. */
 #undef HAVE_MBARRIER_H
 

src/tools/msvc/Solution.pm

@@ -318,7 +318,6 @@ sub GenerateFiles
 		HAVE_LOCALE_T               => 1,
 		HAVE_LONG_INT_64            => undef,
 		HAVE_LONG_LONG_INT_64       => 1,
-		HAVE_LZ4_H                  => undef,
 		HAVE_MBARRIER_H             => undef,
 		HAVE_MBSTOWCS_L             => 1,
 		HAVE_MEMORY_H               => 1,
@@ -541,7 +540,6 @@ sub GenerateFiles
 	if ($self->{options}->{lz4})
 	{
 		$define{HAVE_LIBLZ4} = 1;
-		$define{HAVE_LZ4_H}  = 1;
 		$define{USE_LZ4}     = 1;
 	}
 	if ($self->{options}->{zstd})