cpu-features: Add variant to enable BUILD_SHARED_LIBS=True (#33809)

* Allow building shared libraries for cpu-features

var/spack/repos/builtin/packages/cpu-features/package.py

@@ -17,8 +17,11 @@ class CpuFeatures(CMakePackage):
 
     version("0.7.0", tag="v0.7.0")
 
+    variant("shared", description="Build shared libraries", default=False)
+
     depends_on("cmake@3.0.0:", type="build")
 
     def cmake_args(self):
         args = ["-DBUILD_TESTING:BOOL=OFF"]
+        args += self.enable_or_disable("BUILD_SHARED_LIBS", variant="shared")
         return args