util-linux: fix build failure, add LDFLAGS="-lm"

[jacktose]

This fixes (on my machine) the build failure I reported in discussion #5421. It wasn't linking libm and now it does, with LDFLAGS="-LM", as suggested by @eviatarbach.

It built on the weird CentOS 7 machine where I encountered the error, and it built and tested fine on my normal WSL Ubuntu instance.

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• Have you ensured that your commits follow the commit style guide?
• Have you checked that there aren't other open pull requests for the same formula update/change?
• Have you built your formula locally with HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>, where <formula> is the name of the formula you're submitting?
• Is your test running fine brew test <formula>, where <formula> is the name of the formula you're submitting?
• Does your build pass brew audit --strict <formula> (after doing HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source <formula>)? If this is a new formula, does it pass brew audit --new <formula>?

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Install & test results

$ brew tests
Randomized with seed 11893
20 processes for 399 specs, ~ 19 specs per process
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Pending: (Failures listed here are expected and do not affect your suite's status)

  1) UnpackStrategy::Zip when unzip is available #extract
     # Unzip is not installed.
     # ./test/unpack_strategy/shared_examples.rb:12

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Pending: (Failures listed here are expected and do not affect your suite's status)

  1) UnpackStrategy::Jar is correctly detected
     # Unzip is not installed.
     # ./test/unpack_strategy/shared_examples.rb:6

  2) UnpackStrategy::Jar #extract
     # Unzip is not installed.
     # ./test/unpack_strategy/shared_examples.rb:12

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Took 18 seconds


$ brew uninstall --force util-linux

$ HOMEBREW_NO_INSTALL_FROM_API=1 brew install --build-from-source util-linux
==> Auto-updating Homebrew...
Adjust how often this is run with HOMEBREW_AUTO_UPDATE_SECS or disable with
HOMEBREW_NO_AUTO_UPDATE. Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
==> Fetching util-linux
==> Downloading https://github.com/util-linux/util-linux/commit/9445f477cfcfb3615ffde8f93b1b98c809ee4eca.patch?full_index=1
########################################################################################################################################################################################################## 100.0%
==> Downloading https://mirrors.edge.kernel.org/pub/linux/utils/util-linux/v2.40/util-linux-2.40.4.tar.xz
########################################################################################################################################################################################################## 100.0%
==> Patching
==> Applying 9445f477cfcfb3615ffde8f93b1b98c809ee4eca.patch
==> ./configure --disable-silent-rules --disable-asciidoc --with-bashcompletiondir=/home/linuxbrew/.linuxbrew/Cellar/util-linux/2.40.4/etc/bash_completion.d --disable-use-tty-group --disable-kill --without-sys
==> make install
==> Caveats
Bash completion has been installed to:
  /home/linuxbrew/.linuxbrew/etc/bash_completion.d
==> Summary
🍺  /home/linuxbrew/.linuxbrew/Cellar/util-linux/2.40.4: 443 files, 25.2MB, built in 25 seconds
==> Running `brew cleanup util-linux`...
Disable this behaviour by setting HOMEBREW_NO_INSTALL_CLEANUP.
Hide these hints with HOMEBREW_NO_ENV_HINTS (see `man brew`).
Removing: /home/jacktose/.cache/Homebrew/util-linux--patch--7a7fe4d32806e59f90ca0eb33a9b4eb306e59c9c148493cd6a57f0dea3eafc64.patch... (1.2KB)
==> Installation times
util-linux               25.014 s

$ brew test util-linux
==> Testing util-linux
==> /home/linuxbrew/.linuxbrew/Cellar/util-linux/2.40.4/bin/namei -lx /usr

$ brew audit --strict util-linux

$ brew style util-linux

1 file inspected, no offenses detected