問題

標題の通り。
install出来ない。。

最初のエラー

Last 10 log lines:
checking host system type... x86_64-apple-darwin16.7.0
checking target system type... x86_64-apple-darwin16.7.0
checking whether the C compiler works... yes
checking for C compiler default output file name... a.out
checking for suffix of executables... 
checking whether we are cross compiling... configure: error: in `/var/folders/9s/64j0hkxj5m97r6b6bqf7kx0m0000gn/T/ruby-build.20180225005030.86114/ruby-2.5.0':
configure: error: cannot run C compiled programs.

対応

xcodeを更新
command line tool のアップデート

次のエラー

BUILD FAILED (OS X 10.12.6 using ruby-build 20171226)

Inspect or clean up the working tree at /var/folders/9s/64j0hkxj5m97r6b6bqf7kx0m0000gn/T/ruby-build.20180225012153.25770
Results logged to /var/folders/9s/64j0hkxj5m97r6b6bqf7kx0m0000gn/T/ruby-build.20180225012153.25770.log

Last 10 log lines:
Target: x86_64-apple-darwin16.7.0
Thread model: posix
InstalledDir: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin
compiling miniinit.c
error: error reading '/dev/fd/8'
1 error generated.
clang: error: unable to remove file: Operation not permitted
dtrace: failed to compile script probes.d: Preprocessor failed to process input program
make: *** [probes.h] Error 1
make: *** Waiting for unfinished jobs....

やったこと

sudo chmod -s /usr/sbin/dtrace
https://github.com/rbenv/ruby-build/issues/1061

それでもダメだったので、、
RUBY_CONFIGURE_OPTS="--disable-dtrace" rbenv install 2.5.0