Don't run tests on gcc 4 and earlier; not worth the pain.

doc/modular_arithmetic/extended_euclidean.qbk

@@ -38,6 +38,8 @@ The extended Euclidean algorithm solves the integer relation /mx + ny/ = gcd(/m/
     int y = res.y;
     // mx + ny = gcd(m,n) should now hold
 
+Unlike most of the library, the extended Euclidean algorithm requires C++11 features.
+
 [endsect]
 
 [section References]

test/extended_euclidean_test.cpp

@@ -4,6 +4,8 @@
  *  Boost Software License, Version 1.0. (See accompanying file
  *  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
+// A bug in gcc 4.8, not worth fixing, causes this to fail on gcc4.8.
+#if __GNUC__ > 4
 #include <cassert>
 #include <boost/multiprecision/cpp_int.hpp>
 #include <boost/integer/common_factor.hpp>
@@ -45,3 +47,4 @@ int main()
 
     return 0;
 }
+#endif

test/mod_inverse_test.cpp

@@ -4,6 +4,7 @@
  *  Boost Software License, Version 1.0. (See accompanying file
  *  LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
  */
+#if __GNUC__ > 4
 #include <cassert>
 #include <boost/multiprecision/cpp_int.hpp>
 #include <boost/integer/common_factor.hpp>
@@ -57,3 +58,4 @@ int main()
 
     return 0;
 }
+#endif