memap.py: Allow .a extension for Arm Compiler-generated libraries

The most common extension for static libraries is .a and CMake generates
it with both GCC and Arm toolchains. Mbed CLI 1 generates .ar files with
the Arm Compiler, but since Mbed CLI 2 uses memap.py to generate map
files too, both extensions should be permitted.

This fixes a warning when building greentea tests:

    Malformed input found when parsing ARMCC map: _deps/greentea-client-build/libclient_userio.a(greentea_test_env.o)
    Malformed input found when parsing ARMCC map: _deps/greentea-client-build/libclient_userio.a(greentea_test_env.o)
    Malformed input found when parsing ARMCC map: _deps/greentea-client-build/libclient_userio.a(greentea_test_env.o)
    ...

which repeats over 30 times per test.

Author: LDong-Arm

tools/memap.py

@@ -247,7 +247,7 @@ def parse_mapfile(self, file_desc):
 class _ArmccParser(_Parser):
     RE = re.compile(
         r'^\s+0x(\w{8})\s+0x(\w{8})\s+(\w+)\s+(\w+)\s+(\d+)\s+[*]?.+\s+(.+)$')
-    RE_OBJECT = re.compile(r'(.+\.(l|ar))\((.+\.o(bj)?)\)')
+    RE_OBJECT = re.compile(r'(.+\.(l|a|ar))\((.+\.o(bj)?)\)')
     OBJECT_EXTENSIONS = (".o", ".obj")
 
     def parse_object_name(self, line):