Homebrew で fontconfig が入らなかったときの対応


※自分の環境だけかもしれない

## 発生した問題
どのバージョンからそうなるのかは分からないが、もともと 2.11.0 が入っていた状態から、2.12.1_2 に更新しようとしたら

```
Error: No such file or directory - /usr/local/etc/fonts/conf.d/10-scale-bitmap-fonts.conf
```

と出てしまい、更新できなくなった。

## 原因
調べてみると、該当ファイルがシンボリックリンクになっており、
リンク先が存在しない状態になっていた。  
ちなみに 2.12.1_2 だと、もともとあるファイルは ```<もとのファイル名>.default``` になるようだ。

## 対応
別マシンでは無事だったので、そこから拝借し再度インストール。

## 備考
### エラー全文
```
==> Installing emacs dependency: fontconfig
==> Downloading https://homebrew.bintray.com/bottles/fontconfig-2.12.1_2.sierra.bottle.tar.gz
Already downloaded: /Users/arc680/Library/Caches/Homebrew/fontconfig-2.12.1_2.sierra.bottle.tar.gz
==> Pouring fontconfig-2.12.1_2.sierra.bottle.tar.gz
Error: No such file or directory - /usr/local/etc/fonts/conf.d/10-scale-bitmap-fonts.conf
Warning: Bottle installation failed: building from source.
==> Downloading https://www.freedesktop.org/software/fontconfig/release/fontconfig-2.12.1.tar.bz2
Already downloaded: /Users/arc680/Library/Caches/Homebrew/fontconfig-2.12.1.tar.bz2
==> Downloading https://raw.githubusercontent.com/Homebrew/formula-patches/3790bcd/fontconfig/patch-2.12.1-fccache.diff
Already downloaded: /Users/arc680/Library/Caches/Homebrew/fontconfig--patch-e7c074109a367bf3966578034b20d11f7e0b4a611785a040aef1fd11359af04d.diff
==> Patching
==> Applying patch-2.12.1-fccache.diff
patching file src/fccache.c
==> ./configure --disable-silent-rules --enable-static --with-add-fonts=/System/Library/Fonts,/Library/Fonts,~/Library/Fonts --prefix=/usr/local/Cellar/fontconfig/2.12.1_2 --localstatedir=/usr/local/var -
==> make install RUN_FC_CACHE_TEST=false
Last 15 lines from /Users/arc680/Library/Logs/Homebrew/fontconfig/02.make:
 /usr/bin/install -c -m 644 fc-validate.1 '/usr/local/Cellar/fontconfig/2.12.1_2/share/man/man1'
libtool: install: /usr/bin/install -c .libs/fc-validate /usr/local/Cellar/fontconfig/2.12.1_2/bin/fc-validate
Making install in conf.d
/Library/Developer/CommandLineTools/usr/bin/make  install-am
make[3]: Nothing to be done for `install-exec-am'.
 .././install-sh -c -d '/usr/local/etc/fonts/conf.d'
 .././install-sh -c -d '/usr/local/Cellar/fontconfig/2.12.1_2/share/fontconfig/conf.avail'
 /usr/bin/install -c -m 644 README '/usr/local/etc/fonts/conf.d'
install: /usr/local/etc/fonts/conf.d/README: No such file or directory
make[3]: *** [install-configDATA] Error 71
make[3]: *** Waiting for unfinished jobs....
 /usr/bin/install -c -m 644 10-autohint.conf 10-hinting-full.conf 10-hinting-medium.conf 10-hinting-none.conf 10-hinting-slight.conf 10-no-sub-pixel.conf 10-scale-bitmap-fonts.conf 10-sub-pixel-bgr.conf 10-sub-pixel-rgb.conf 10-sub-pixel-vbgr.conf 10-sub-pixel-vrgb.conf 10-unhinted.conf 11-lcdfilter-default.conf 11-lcdfilter-legacy.conf 11-lcdfilter-light.conf 20-unhint-small-vera.conf 25-unhint-nonlatin.conf 30-urw-aliases.conf 30-metric-aliases.conf 40-nonlatin.conf 45-latin.conf 49-sansserif.conf 50-user.conf 51-local.conf 60-latin.conf 65-fonts-persian.conf 65-khmer.conf 65-nonlatin.conf 69-unifont.conf 70-no-bitmaps.conf 70-yes-bitmaps.conf 80-delicious.conf 90-synthetic.conf '/usr/local/Cellar/fontconfig/2.12.1_2/share/fontconfig/conf.avail'
make[2]: *** [install-am] Error 2
make[1]: *** [install] Error 2
make: *** [install-recursive] Error 1

READ THIS: https://git.io/brew-troubleshooting
If reporting this issue please do so at (not Homebrew/brew):
  https://github.com/Homebrew/homebrew-core/issues
```