\[ \boxed { \sqrt {-{x}^{2}+1}{\frac {\rm d}{{\rm d}x}}y \left ( x \right ) -y \left ( x \right ) \sqrt { \left ( y \left ( x \right ) \right ) ^{2}-1}=0} \]
Mathematica: cpu = 0.030004 (sec), leaf count = 52 \[ \left \{\left \{y(x)\to \sqrt {\tan ^2\left (c_1+\sin ^{-1}(x)\right )+1} \left (-\cot \left (c_1+\sin ^{-1}(x)\right )\right )\right \},\left \{y(x)\to \sqrt {\tan ^2\left (c_1+\sin ^{-1}(x)\right )+1} \cot \left (c_1+\sin ^{-1}(x)\right )\right \}\right \} \]
Maple: cpu = 0.015 (sec), leaf count = 16 \[ \left \{ \arcsin \left ( x \right ) +\arctan \left ( {\frac {1}{\sqrt { \left ( y \left ( x \right ) \right ) ^{2}-1}}} \right ) +{\it \_C1}=0 \right \} \]