krb5: added 'shared' variant and support to build static library (#20017)

Co-authored-by: Massimiliano Culpo <massimiliano.culpo@gmail.com>

var/spack/repos/builtin/packages/krb5/mit-krb5-1.17-static-libs.patch

@@ -0,0 +1,15 @@
+--- src/lib/crypto/builtin/aes/Makefile.in.orig	2019-06-27 14:51:51.305688932 +0200
++++ src/lib/crypto/builtin/aes/Makefile.in	2019-06-27 14:52:46.428203235 +0200
+@@ -34,10 +34,10 @@
+ 
+ all-unix: all-libobjs # aes-gen
+ 
+-iaesx64@SHOBJEXT@: $(srcdir)/iaesx64.s
++iaesx64.$(OBJEXT) iaesx64@SHOBJEXT@: $(srcdir)/iaesx64.s
+ 	$(YASM) $(AESNI_FLAGS) -o $@ $(srcdir)/iaesx64.s
+ 
+-iaesx86@SHOBJEXT@: $(srcdir)/iaesx86.s
++iaesx86.$(OBJEXT) iaesx86@SHOBJEXT@: $(srcdir)/iaesx86.s
+ 	$(YASM) $(AESNI_FLAGS) -o $@ $(srcdir)/iaesx86.s
+ 
+ includes: depend

var/spack/repos/builtin/packages/krb5/package.py

@@ -26,6 +26,12 @@ class Krb5(AutotoolsPackage):
     depends_on('bison', type='build')
     depends_on('openssl')
 
+    variant(
+        'shared', default=True,
+        description='install shared libraries if True, static if false'
+    )
+    patch('mit-krb5-1.17-static-libs.patch', level=0)
+
     configure_directory = 'src'
     build_directory = 'src'
 
@@ -51,4 +57,12 @@ def patch(self):
             string=True)
 
     def configure_args(self):
-        return ['--without-system-verto']
+        args = ['--without-system-verto']
+
+        if '~shared' in self.spec:
+            args.append('--enable-static')
+            args.append('--disable-shared')
+        else:
+            args.append('--disable-static')
+
+        return args