Add old version to bcftools (#5907)

* bcftools v1.2 and htslib v1.2

* dependency change - only require dependencies for v1.2

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

@@ -37,10 +37,12 @@ class Bcftools(Package):
     version('1.6', 'c4dba1e8cb55db0f94b4c47724b4f9fa')
     version('1.4', '50ccf0a073bd70e99cdb3c8be830416e')
     version('1.3.1', '575001e9fca37cab0c7a7287ad4b1cdb')
+    version('1.2', '8044bed8fce62f7072fc6835420f0906')
 
     depends_on('htslib@1.6',   when='@1.6')
     depends_on('htslib@1.4',   when='@1.4')
     depends_on('htslib@1.3.1', when='@1.3.1')
+    depends_on('htslib@1.2', when='@1.2')
 
     def install(self, spec, prefix):
         make("prefix=%s" % prefix, "all")