compilers/clang: add flang (#5503)

* compilers/clang: add flang

* Update clang.py

lib/spack/env/cc

@@ -110,13 +110,13 @@ case "$command" in
         comp="CXX"
         lang_flags=CXX
         ;;
-    ftn|f90|fc|f95|gfortran|ifort|pgfortran|xlf90|xlf90_r|nagfor)
+    ftn|f90|fc|f95|gfortran|flang|ifort|pgfortran|xlf90|xlf90_r|nagfor)
         command="$SPACK_FC"
         language="Fortran 90"
         comp="FC"
         lang_flags=F
         ;;
-    f77|gfortran|ifort|pgfortran|xlf|xlf_r|nagfor|ftn)
+    f77|gfortran|flang|ifort|pgfortran|xlf|xlf_r|nagfor|ftn)
         command="$SPACK_F77"
         language="Fortran 77"
         comp="F77"

lib/spack/env/clang/flang

@@ -0,0 +1 @@
+../cc

lib/spack/spack/compilers/clang.py

@@ -42,18 +42,23 @@ class Clang(Compiler):
     cxx_names = ['clang++']
 
     # Subclasses use possible names of Fortran 77 compiler
-    f77_names = ['gfortran']
+    f77_names = ['flang', 'gfortran']
 
     # Subclasses use possible names of Fortran 90 compiler
-    fc_names = ['gfortran']
+    fc_names = ['flang', 'gfortran']
 
     # Named wrapper links within spack.build_env_path
     link_paths = {'cc': 'clang/clang',
-                  'cxx': 'clang/clang++',
+                  'cxx': 'clang/clang++'}
+
+    if sys.platform == 'darwin':
         # Use default wrappers for fortran, in case provided in
         # compilers.yaml
-                  'f77': 'clang/gfortran',
-                  'fc': 'clang/gfortran'}
+        link_paths['f77'] = 'clang/gfortran'
+        link_paths['fc'] = 'clang/gfortran'
+    else:
+        link_paths['f77'] = 'clang/flang'
+        link_paths['fc'] = 'clang/flang'
 
     @property
     def is_apple(self):
@@ -169,7 +174,7 @@ def fc_version(cls, fc):
         if sys.platform == 'darwin':
             return cls.default_version('clang')
         else:
-            return 'unknown'
+            return cls.default_version(fc)
 
     @classmethod
     def f77_version(cls, f77):