base, systemc: Fix clang compilation

This patch is fixing the following issues:

- base: typename should be used only for types
- systemc: 'GCC_VERSION' is not defined for clang

Change-Id: I27c94445d65691a08a0a14a0ffe6b6942f6c455f
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/14976
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Gabe Black <gabeblack@google.com>

src/systemc/SConscript

@@ -31,7 +31,9 @@ from m5.util import compareVersions
 from m5.util.terminal import termcap
 
 if env['USE_SYSTEMC']:
-    if compareVersions(env['GCC_VERSION'], '5.0') < 0:
+    if 'GCC_VERSION' in env and \
+        compareVersions(env['GCC_VERSION'], '5.0') < 0:
+
         print(termcap.Yellow + termcap.Bold +
                 'Warning: Disabling systemc on gcc versions less than 5.0.' +
                 termcap.Normal)