[fix][upwindscheme] Use using std::signbit to allow for ADL
(cherry picked from commit 745553c6)
The problem came up in !2401 (closed). This backport should fix this problem for the release branch.
Edited by Timo Koch
(cherry picked from commit 745553c6)
The problem came up in !2401 (closed). This backport should fix this problem for the release branch.