fix building tests when char is unsigned

when char is unsigned it's uint8_t which doesn't match the type declared
for the key of the map, so it fails with

error: non-constant-expression cannot be narrowed from type
'typename std::enable_if<std::is_integral<char>::value && sizeof(char) == sizeof(char), char>::type'
(aka 'char') to 'const signed char' in initializer list

etc

Author: nekopsykose

unittests/map.hpp

@@ -62,7 +62,7 @@ void test_map()
 
     std::map<int8_t, StructExternalSplit> o_esplmap;
     for(int j=0; j<100; ++j)
-      o_esplmap.insert({random_value<char>(gen),  { random_value<int>(gen), random_value<int>(gen) }});
+      o_esplmap.insert({random_value<int8_t>(gen),  { random_value<int>(gen), random_value<int>(gen) }});
 
     std::ostringstream os;
     {

unittests/multimap.hpp

@@ -71,7 +71,7 @@ void test_multimap()
     std::multimap<int8_t, StructExternalSplit> o_esplmultimap;
     for(int j=0; j<100; ++j)
     {
-      auto key = random_value<char>(gen);
+      auto key = random_value<int8_t>(gen);
       o_esplmultimap.insert({key,  { random_value<int>(gen), random_value<int>(gen) }});
       o_esplmultimap.insert({key,  { random_value<int>(gen), random_value<int>(gen) }});
     }

unittests/unordered_map.hpp

@@ -54,7 +54,7 @@ void test_unordered_map()
 
     std::unordered_map<int8_t, StructExternalSplit> o_esplunordered_map;
     for(int j=0; j<100; ++j)
-      o_esplunordered_map.insert({random_value<char>(gen),  { random_value<int>(gen), random_value<int>(gen) }});
+      o_esplunordered_map.insert({random_value<int8_t>(gen),  { random_value<int>(gen), random_value<int>(gen) }});
 
     std::ostringstream os;
     {

unittests/unordered_multimap.hpp

@@ -71,7 +71,7 @@ void test_unordered_multimap()
     std::unordered_multimap<int8_t, StructExternalSplit> o_esplunordered_multimap;
     for(int j=0; j<100; ++j)
     {
-      auto key = random_value<char>(gen);
+      auto key = random_value<int8_t>(gen);
       o_esplunordered_multimap.insert({key,  { random_value<int>(gen), random_value<int>(gen) }});
       o_esplunordered_multimap.insert({key,  { random_value<int>(gen), random_value<int>(gen) }});
     }