IE11 supports the transform attribute in SVG even though it doesn't recognize the CSS style.
Fortunately, you can simply set the attribute to match the style using JavaScript:
var g = document.querySelector('.st8'),
transform = getComputedStyle(g).getPropertyValue('transform');
g.setAttribute('transform', transform);
.st8 {
-ms-transform: rotate(45deg); /* doesn't work on IE */
transform: rotate(45deg);
}
<svg>
<path class='st8' d='M73.4,11.3c-6.3,0-6.4,3.6-6.4,3.6v18c0,0,0.6,3.3,6.4,3.3c5.8,0,6.6-3.3,6.6-3.3v-18 C80,14.9,79.7,11.3,73.4,11.3z M75,31.3c0,0-0.3,1.2-1.6,1.2c-1.3,0-1.4-1.2-1.4-1.2V16.6c0,0,0.3-1.3,1.5-1.3s1.5,1.3,1.5,1.3V31.3 z'/>
</svg>
Although IE9+ support CSS3 transforms, they don't support them on SVG and to the best on my knowledge it can't be done in CSS.
source: caniuse under known issues for CSS3 Transforms http://caniuse.com/#feat=transforms2d