Meaning of $\geqslant$, $\leqslant$, $\eqslantgtr$, $\eqslantless$

$\geqslant$ is an alternative to $\geq$ and means the same: $a \geqslant b$ = "$a$ is greater than or equal to $b$".

Likewise, $\leqslant$ is an alternative notation for $\leq$, with $a \leqslant b$ = "$a$ is less than or equal to $b$".

I haven't encountered $\eqslantgtr$ or $\eqslantless$, but given that the former is formatted eqslantgtr and the latter eqslantless, I would venture to guess that they likewise denote "greater than or equal to" and "less than or equal to", respectively. Perhaps with these symbols, where the emphasis appears to be on the "equals" component, they are read as "equal to or greater than" and "equal to or less than", respectively.

In Russia $\geqslant$ and $\leqslant$ are used instead of $\geq$ and $\leq$.
We don't use $\geq$ and $\leq$ at all.
But I've never seen $\eqslantgtr$ and $\eqslantless$ in Russian math texts.

P.S.
1. There are more interesting distinctions between Russian and English math notations.
For example, we occasionally using $\ n\vdots d\ $ instead of $\ d|n$.
2. There are a lot of strange math symbols exists: see here and here.