hpctoolkit: adjust libunwind dependency (#15099)

Change hpctoolkit's dependency on libunwind from 2018.10.12 to 1.4:.
In libunwind, 2018.10.12 is going away in favor of 1.4-rc1 (they're
nearly identical commits).

Remove the 'gpu' version.  This was a temporary branch that is now
folded into master.

var/spack/repos/builtin/packages/hpctoolkit/package.py

@@ -19,7 +19,6 @@ class Hpctoolkit(AutotoolsPackage):
     maintainers = ['mwkrentel']
 
     version('master', branch='master')
-    version('gpu', branch='gpu')
     version('2019.12.28', commit='b4e1877ff96069fd8ed0fdf0e36283a5b4b62240')
     version('2019.08.14', commit='6ea44ed3f93ede2d0a48937f288a2d41188a277c')
     version('2018.12.28', commit='8dbf0d543171ffa9885344f32f23cc6f7f6e39bc')
@@ -53,7 +52,7 @@ class Hpctoolkit(AutotoolsPackage):
             'for the compute nodes.')
 
     variant('cuda', default=False,
-            description='Support CUDA on NVIDIA GPUs (master or gpu branch).')
+            description='Support CUDA on NVIDIA GPUs (master branch).')
 
     boost_libs = (
         '+atomic +chrono +date_time +filesystem +system +thread +timer'
@@ -69,7 +68,7 @@ class Hpctoolkit(AutotoolsPackage):
     depends_on('libdwarf')
     depends_on('libmonitor+hpctoolkit')
     depends_on('libmonitor+bgq', when='+bgq')
-    depends_on('libunwind@2018.10.0:')
+    depends_on('libunwind@1.4:')
     depends_on('mbedtls+pic')
     depends_on('xerces-c transcoder=iconv')
     depends_on('xz', type='link')
@@ -84,14 +83,11 @@ class Hpctoolkit(AutotoolsPackage):
     conflicts('%gcc@:4.7.99', when='^dyninst@10.0.0:',
               msg='hpctoolkit requires gnu gcc 4.8.x or later')
 
-    conflicts('%gcc@:4.99.99', when='@gpu',
-              msg='the gpu branch requires gnu gcc 5.x or later')
-
     conflicts('%gcc@:4.99.99', when='@master',
               msg='the master branch requires gnu gcc 5.x or later')
 
     conflicts('+cuda', when='@2018.0.0:2019.99.99',
-              msg='cuda is only available on the master or gpu branches')
+              msg='cuda is only available on the master branch')
 
     flag_handler = AutotoolsPackage.build_system_flags