Fixes#6590
The ASM block that implements the read-uint32-unaligned returns a
uint32_t. The old code was doing a cast like `(float)(uint32_t ret)
which actually goes and creates a new float of the positive uint value
(approx, of course due to exponent and sign bits) which is not correct.
C and C++ don't have a concise way to convert the bits in a register
from int to float interpretation, so avoid the whole issue by making a
new function which uses the same ASM block as the read-uint32-unaligned,
just make the destination and return values as floats.
fb2cbe36a1