Unable to install Ruby 2.6.3 on macOS 10.14.5 Mojave

[DoctorofTheEARTH]

help me....
This is the first time to install Ruby.
when I run "rbenv install 2.6.3," this happens.
I cannot figure the solution out.
what steps do I have to fix it??

ruby-build: use openssl from homebrew
Downloading ruby-2.6.3.tar.bz2...
-> https://cache.ruby-lang.org/pub/ruby/2.6/ruby-2.6.3.tar.bz2
Installing ruby-2.6.3...

BUILD FAILED (OS X 10.14.5 using ruby-build 20190423)

Inspect or clean up the working tree at /var/folders/ss/t826qgw50bg9_k1vdfq1q2940000gn/T/ruby-build.20190802010118.21626
Results logged to /var/folders/ss/t826qgw50bg9_k1vdfq1q2940000gn/T/ruby-build.20190802010118.21626.log

Last 10 log lines:
tool/config.guess already exists
tool/config.sub already exists
checking build system type... x86_64-apple-darwin18.6.0
checking host system type... x86_64-apple-darwin18.6.0
checking target system type... x86_64-apple-darwin18.6.0
checking whether the C compiler works... no
configure: error: in /var/folders/ss/t826qgw50bg9_k1vdfq1q2940000gn/T/ruby-build.20190802010118.21626/ruby-2.6.3': configure: error: C compiler cannot create executables See config.log' for more details
make: *** No targets specified and no makefile found. Stop.

[mislav]

I'm sorry you have had trouble. I don't know what causes this, but see other threads: #1364 #1203 #1193 #779 #640 #353 #319