Use BOOST_IF_CONSTEXPR to avoid warnings

Author: Flamefire

test/test_encoding.cpp

@@ -49,7 +49,7 @@ static MacOSIconvIssue isFaultyIconv()
 static bool iConvUsesWTF8()
 {
     // The test uses a 4-byte value
-    if(sizeof(wchar_t) != 4)
+    BOOST_IF_CONSTEXPR(sizeof(wchar_t) != 4)
         return false;
     iconv_t cd = iconv_open("UTF-8", boost::locale::util::utf_name<wchar_t>());
     if(cd == (iconv_t)-1)
@@ -395,12 +395,12 @@ void test_utf_for()
     }
     const auto iconvIssue = isFaultyIconv();
     // Testing a codepage which may crash with IConv on macOS, see issue #196
-    if(iconvIssue != MacOSIconvIssue::InfiniteLoop)
+    BOOST_IF_CONSTEXPR(iconvIssue != MacOSIconvIssue::InfiniteLoop)
         test_to_from_utf<Char>("\xa1\xad\xa1\xad", utf<Char>("……"), "gbk", false);
 
     // This might cause a bogus E2BIG with Apples Iconv, see issue #206
     // If it does not it might not have proper ISO-2022-CN support and returns wrong results
-    if(iconvIssue != MacOSIconvIssue::No_CN_Support)
+    BOOST_IF_CONSTEXPR(iconvIssue != MacOSIconvIssue::No_CN_Support)
         test_to_from_utf<Char>("\x1b\x24\x29\x41\x0e\x4a\x35\xf", utf<Char>("实"), "ISO-2022-CN", false);
 
     std::cout << "- Testing correct invalid bytes skipping\n";