By the tiniest of margins, 115. Deleted two spaces and an `l`. Largely inspired by `svgo`. Using `rsvg-convert` to render them both to PNG shows identical output between this and the 118 version. https://rjp.is/hn-svg.html seems to render them identically in Safari and Chrome.
That appears to be trigged by "-32-32" (broken) vs "-32 -32" (working). Looks like this has been a long-standing weirdness in Firefox[1] where it is allowed somewhere but not other places.
On the other hand, the spec[2] does specify whitespace or commas between the viewbox numbers.
Oh, if you then switch to the comma-style for viewBox, drop the / from the path tag, and drop the quotes from the style attributes, that takes it down to 109.
Safari, Chrome, and Firefox are all perfectly happy with it but then rsvg-convert chokes on all of those changes. 114 is probably the best that can be done and still be "conforming" (for want of a better word.)
<svg viewBox="-32 -32 64 64" style="background: #f60"><path fill="#fff" d="m0-5l-8-12h-7L-3 1v16h6V1l12-18H8z"/></svg>