assimp: fix compile issues with intel compilers on knl/linux [a depen… (#9191)

* assimp: fix compile issues with intel compilers on knl/linux [a dependency for dealii]

Fixes issue #9189

* assimp: add variant 'shared' with default value 'True'

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

@@ -34,8 +34,21 @@ class Assimp(CMakePackage):
 
     version('4.0.1', '23a6301c728a413aafbfa1cca19ba91f')
 
+    variant('shared',  default=True,
+            description='Enables the build of shared libraries')
+
     depends_on('boost')
 
     def cmake_args(self):
-        args = ['-DASSIMP_BUILD_TESTS=OFF']
+        args = [
+            '-DASSIMP_BUILD_TESTS=OFF',
+            '-DBUILD_SHARED_LIBS:BOOL=%s' % (
+                'ON' if '+shared' in self.spec else 'OFF'),
+        ]
         return args
+
+    def flag_handler(self, name, flags):
+        flags = list(flags)
+        if name == 'cxxflags':
+            flags.append(self.compiler.cxx11_flag)
+        return (None, None, flags)