Add optional enable_64bit_file_offset

Author: LawrenceHunter

configure.ac

@@ -50,6 +50,7 @@ PKG_PROG_PKG_CONFIG
 ACX_PEDANTIC
 ACX_STRICT
 ACX_64BIT
+ACX_64BIT_FILE_OFFSET
 AX_CXX_COMPILE_STDCXX_11([noext],[optional])
 
 # Check for libraries (-ldl can be required by OpenSSL too)

m4/acx_64bit_file_offset.m4

@@ -0,0 +1,13 @@
+AC_DEFUN([ACX_64BIT_FILE_OFFSET],[
+	AC_ARG_ENABLE(
+		[64bit_file_offset],
+		[AS_HELP_STRING([--enable-64bit-file-offset],[enable 64 bit file offset mode @<:@disabled@:>@])],
+		,
+        [enable_64bit_file_offset="${enableval}"],
+        [enable_64bit_file_offset="no"]
+	)
+	if test "${enable_64bit_file_offset}" = "yes"; then
+		CFLAGS="${CFLAGS} -D_FILE_OFFSET_BITS=64"
+		CXXFLAGS="${CXXFLAGS} -D_FILE_OFFSET_BITS=64"
+	fi
+])