rts: Properly free the RTSSummaryStats structure

`stat_exit` always allocates a `RTSSummaryStats` but only sometimes
frees it, which casues leaks. With this patch we unconditionally free
the structure, fixing the leak.

Fixes #16584
19 jobs for master in 237 minutes and 55 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  Lint
passed #74216
lint
lint-submods

00:01:17

 
  Build
passed #74218
x86_64-linux
hadrian-ghc-in-ghci

00:25:53

failed #74220
x86_64-linux allowed to fail
release-x86_64-linux-deb9-dwarf

01:05:12

failed #74217
x86_64-linux allowed to fail
validate-x86_64-linux-deb8-hadrian

01:32:43

passed #74219
x86_64-linux
validate-x86_64-linux-deb9-debug

00:56:42

 
  Full Build
failed #74222
aarch64-linux allowed to fail
validate-aarch64-linux-deb9

01:04:22

passed #74223
x86_64-linux
validate-i386-linux-deb9

01:16:32

passed #74221
x86_64-darwin
validate-x86_64-darwin

00:56:40

passed #74224
x86_64-linux
validate-x86_64-linux-deb9

01:21:17

passed #74226
x86_64-linux
validate-x86_64-linux-deb9-integer-simple

01:23:24

passed #74225
x86_64-linux
validate-x86_64-linux-deb9-llvm

02:19:07

passed #74227
x86_64-linux
validate-x86_64-linux-deb9-unreg

02:23:30

passed #74228
x86_64-linux
validate-x86_64-linux-fedora27

01:25:43

failed #74229
x86_64-windows allowed to fail
validate-x86_64-windows

02:12:47

 
  Cleanup
passed #74231
x86_64-darwin
cleanup-darwin

00:00:05

failed #74230
x86_64-windows
cleanup-windows

00:00:18

 
  Packaging
skipped #74232
x86_64-linux allowed to fail
doc-tarball
 
  Hackage
skipped #74233
x86_64-linux allowed to fail manual
hackage
 
  Deploy
skipped #74234
x86_64-linux allowed to fail
pages
 
Name Stage Failure
failed
validate-x86_64-linux-deb8-hadrian Build
Exit code: 1
Stderr:
)


Uploading artifacts...
junit.xml: found 1 matching files
Uploading artifacts to coordinator... ok
id=74217 responseStatus=201 Created token=3irqibTk
ERROR: Job failed: exit code 1
failed
validate-x86_64-windows Full Build
junit.xml: found 1 matching files                  
WARNING: Failed to load system CertPool: crypto/x509: system root pool is not available on Windows
Uploading artifacts to coordinator... ok
id=74229 responseStatus=201 Created token=esrxmjzb
Uploading artifacts...
Runtime platform
arch=amd64 os=windows pid=4572 revision=7f00c780 version=11.5.1
junit.xml: found 1 matching files

WARNING: Failed to load system CertPool: crypto/x509: system root pool is not available on Windows
Uploading artifacts to coordinator... ok
id=74229 responseStatus=201 Created token=esrxmjzb
ERROR: Job failed: exit status 2
failed
validate-aarch64-linux-deb9 Full Build
$ cp -Rf $HOME/.cabal cabal-cache
Uploading artifacts...
WARNING: ghc-*.tar.xz: no matching files
WARNING: junit.xml: no matching files
ERROR: No files to upload
Uploading artifacts...
WARNING: junit.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1
failed
cleanup-windows Cleanup
Checking out f862963b as master...
fatal: Unable to create 'C:/GitLabRunner/builds/pA2hwqzM/0/ghc/ghc/.git/index.lock': File exists.

Another git process seems to be running in this repository, e.g.
an editor opened by 'git commit'. Please make sure all processes
are terminated then try again. If it still fails, a git process
may have crashed in this repository earlier:
remove the file manually to continue.
ERROR: Job failed: exit status 128
failed
release-x86_64-linux-deb9-dwarf Build
$ cp -Rf $HOME/.cabal cabal-cache
Uploading artifacts...
ghc-*.tar.xz: found 1 matching files
junit.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=74220 responseStatus=201 Created token=nA-ibepb
Uploading artifacts...
junit.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=74220 responseStatus=201 Created token=nA-ibepb
ERROR: Job failed: exit code 1