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 +1,12 @@
+AC_DEFUN([ACX_64BIT_FILE_OFFSET],[
+	AC_ARG_ENABLE(
+		[strict],
+		[AS_HELP_STRING([--enable_64bit_file_offset],[enable 64 bit file offset mode @<:@enabled@:>@])],
+		,
+		[enable_64bit_file_offset="yes"]
+	)
+	if test "${enable_64bit_file_offset}" = "yes"; then
+		CFLAGS="${CFLAGS} -D_FILE_OFFSET_BITS=64"
+		CXXFLAGS="${CXXFLAGS} -D_FILE_OFFSET_BITS=64"
+	fi
+])