warpx: only allow master branch, and fix build on darwin (#11667)

* warpx: only allow master branch, and fix build on darwin

* warpx: Added CXXFLAGS=-std=c++11 for clang

* warpx: further clean up of openmp and c++11 flags

* warpx: Get around the problem with resources

The update uses placement instead of destination

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

@@ -4,6 +4,7 @@
 # SPDX-License-Identifier: (Apache-2.0 OR MIT)
 
 from spack import *
+from spack.compiler import UnsupportedCompilerFlag
 
 
 class Warpx(MakefilePackage):
@@ -38,13 +39,27 @@ class Warpx(MakefilePackage):
 
     resource(name='amrex',
              git='https://github.com/AMReX-Codes/amrex.git',
+             when='@master',
+             tag='master',
+             placement='amrex')
+
+    resource(name='amrex',
+             git='https://github.com/AMReX-Codes/amrex.git',
+             when='@dev',
              tag='development',
-             destination='.')
+             placement='amrex')
 
     resource(name='picsar',
              git='https://bitbucket.org/berkeleylab/picsar.git',
              tag='master',
-             destination='.')
+             placement='picsar')
+
+    @property
+    def build_targets(self):
+        if self.spec.satisfies('%clang'):
+            return ['CXXFLAGS={0}'.format(self.compiler.cxx11_flag)]
+        else:
+            return []
 
     def edit(self, spec, prefix):
 
@@ -68,8 +83,14 @@ def torf(s):
                         'USE_PSATD = {0}'.format(torf('+psatd')))
         makefile.filter('DO_ELECTROSTATIC .*',
                         'DO_ELECTROSTATIC = %s' % torf('+do_electrostatic'))
+        try:
+            self.compiler.openmp_flag
+        except UnsupportedCompilerFlag:
+            use_omp = 'FALSE'
+        else:
+            use_omp = torf('+openmp')
         makefile.filter('USE_OMP .*',
-                        'USE_OMP = {0}'.format(torf('+openmp')))
+                        'USE_OMP = {0}'.format(use_omp))
         makefile.filter('DEBUG .*',
                         'DEBUG = {0}'.format(torf('+debug')))
         makefile.filter('TINY_PROFILE .*',