Speedup Travis CI: stop smoking on Darwin

Resolves #17209

A full Travis CI build time is about 4 hours,
most of the time is spent on osx servers.

Travis CI does not seem to have the same kind
of resources for Darwin than it has for linux.

Disabling Darwin will speedup the builds to ~15 min

Also enable fast finish to stop on first failure.

.travis.yml

@@ -3,11 +3,9 @@ cache: ccache
 
 os:
   - linux
-  - osx
 
 compiler:
   - gcc
-  - clang
 
 install:
   - git fetch --unshallow --tags # t/porting/cmp_version.t
@@ -24,10 +22,10 @@ env:
         - CONFIGURE_ARGS='-DPERL_GLOBAL_STRUCT'
         - CONFIGURE_ARGS='-DPERL_GLOBAL_STRUCT_PRIVATE'
         - CONFIGURE_ARGS='-Duseshrplib -Dusesitecustomize'
-        - CONFIGURE_ARGS='-Duserelocatableinc'
 
 # only use gcc on linux, and only use clang on osx for now
 matrix:
+  fast_finish: true
   exclude:
   - compiler: clang
     os: linux