Move sys_libs into mbedToolchain class

tools/toolchains/__init__.py

@@ -266,6 +266,9 @@ class mbedToolchain:
         # Toolchain flags
         self.flags = deepcopy(build_profile or self.profile_template)
 
+        # System libraries provided by the toolchain
+        self.sys_libs = []
+
         # User-defined macros
         self.macros = macros or []
 

tools/toolchains/arm.py

@@ -66,7 +66,6 @@ class ARM(mbedToolchain):
         self.cppc = [main_cc] + self.flags['common'] + self.flags['c'] + self.flags['cxx']
 
         self.ld = [join(ARM_BIN, "armlink")]
-        self.sys_libs = []
 
         self.ar = join(ARM_BIN, "armar")
         self.elf2bin = join(ARM_BIN, "fromelf")