Add test for overflow in expt that shouldn't happen

We shouldn't get an overflow, but we do because clang 10 miscompiles
e_pow.c and causes an overflow.

Addresses #101
8 jobs for issue-101-add-test in 23 minutes and 41 seconds (queued for 3 seconds)
latest
Status Job ID Name Coverage
  Install
passed #9026
linux
linux:install

00:00:54

passed #9027
osx
osx:install

00:01:01

 
  Build
passed #9028
linux
linux:build

00:05:51

passed #9029
osx
osx:build

00:12:43

 
  Test
passed #9030
linux
linux:test

00:02:35

passed #9031
osx
osx:test

00:04:58

 
  Benchmark
passed #9032
linux
linux:benchmark

00:02:56

passed #9033
osx
osx:benchmark

00:04:57