$ which gcc
/bin/gcc

$ g++-5 --version
-bash: g++-5: command not found

$ sudo find /usr -name gcc-5
$ sudo find /bin -name gcc-5
$

$ sudo pkg install --accept gcc-5
------------------------------------------------------------
Package: pkg://solaris/release/evaluation@1.0,5.12-5.12.0.0.0.115.0:20170111T175931Z
License: evaluation

This software has been made available for evaluation purposes only.
See http://www.oracle.com/technetwork/server-storage/solaris11/technologies/foss-evaluation-program-2586275.html for further information.

           Packages to install:  2
       Create boot environment: No
Create backup boot environment: No

DOWNLOAD                                PKGS         FILES    XFER (MB)   SPEED
Completed                                2/2           8/8      0.0/0.0 17.4k/s

PHASE                                          ITEMS
Installing new actions                         37/37
Updating package state database                 Done
Updating package cache                           0/0
Updating image state                            Done
Creating fast lookup database                   Done
Updating package cache                           2/2

gcc --version

gcc-5 --version