Common/Utilities: ported StringConvert helpers from 335 branch

cmake/compiler/clang/settings.cmake

@@ -13,6 +13,31 @@ else()
   message(STATUS "Clang: Minimum version required is ${CLANG_EXPECTED_VERSION}, found ${CMAKE_CXX_COMPILER_VERSION} - ok!")
 endif()
 
+# This tests for a bug in clang-7 that causes linkage to fail for 64-bit from_chars (in some configurations)
+# If the clang requirement is bumped to >= clang-8, you can remove this check, as well as
+# the associated ifdef block in src/common/Utilities/StringConvert.h
+include(CheckCXXSourceCompiles)
+
+check_cxx_source_compiles("
+#include <charconv>
+#include <cstdint>
+
+int main()
+{
+    uint64_t n;
+    char const c[] = \"0\";
+    std::from_chars(c, c+1, n);
+    return static_cast<int>(n);
+}
+" CLANG_HAVE_PROPER_CHARCONV)
+
+if (NOT CLANG_HAVE_PROPER_CHARCONV)
+  message(STATUS "Clang: Detected from_chars bug for 64-bit integers, workaround enabled")
+  target_compile_definitions(trinity-compile-option-interface
+          INTERFACE
+          TRINITY_NEED_CHARCONV_WORKAROUND)
+endif()
+
 if(WITH_WARNINGS)
   target_compile_options(trinity-warning-interface
     INTERFACE