[build] Silence compilation warnings

Do not use the same buffer for readlink() input and output.

Add missing "fall through" comments and tell gcc to be less
strict about wording / capitalization of existing ones.

Signed-off-by: Simo Piiroinen <simo.piiroinen@jollamobile.com>

Makefile

@@ -262,6 +262,7 @@ CFLAGS += -Wstack-protector
 #CFLAGS += -Werror (OBS build might have different compiler)
 CFLAGS += -Wno-declaration-after-statement
 CFLAGS += -Wno-missing-field-initializers
+CFLAGS += -Wimplicit-fallthrough=2
 
 # Linker
 LDLIBS   += -Wl,--as-needed

evdev.c

@@ -2,7 +2,8 @@
  * @file evdev.c
  * Mode Control Entity - evdev input device handling
  * <p>
- * Copyright (C) 2012-2019 Jolla Ltd.
+ * Copyright (c) 2012 - 2020 Jolla Ltd.
+ * Copyright (c) 2020 Open Mobile Platform LLC.
  * <p>
  * @author Simo Piiroinen <simo.piiroinen@jollamobile.com>
  *
@@ -262,16 +263,17 @@ int evdev_identify_device(int fd)
   unsigned long bmap_type[BMAP_SIZE(EV_CNT)];
   unsigned long bmap_code[BMAP_SIZE(KEY_CNT)];
   unsigned long bmap_stat[BMAP_SIZE(KEY_CNT)];
-  char path[256];
+  char linkpath[PATH_MAX];
+  char path[PATH_MAX];
   int n;
 
   if( fd < 0 )
   {
     goto cleanup;
   }
 
-  snprintf(path, sizeof path, "/proc/self/fd/%d", fd);
-  if( (n = readlink(path, path, sizeof path - 1)) <= 0 )
+  snprintf(linkpath, sizeof linkpath, "/proc/self/fd/%d", fd);
+  if( (n = readlink(linkpath, path, sizeof path - 1)) <= 0 )
   {
     strcpy(path, "unknown");
   }

event-input.c

@@ -2,8 +2,9 @@
  * @file event-input.c
  * /dev/input event provider for the Mode Control Entity
  * <p>
- * Copyright © 2004-2011 Nokia Corporation and/or its subsidiary(-ies).
- * Copyright (C) 2013-2019 Jolla Ltd.
+ * Copyright (c) 2004 - 2011 Nokia Corporation and/or its subsidiary(-ies).
+ * Copyright (c) 2013 - 2020 Jolla Ltd.
+ * Copyright (c) 2020 Open Mobile Platform LLC.
  * <p>
  * @author David Weinehall <david.weinehall@nokia.com>
  * @author Ismo Laitinen <ismo.laitinen@nokia.com>
@@ -3542,6 +3543,7 @@ evin_datapipe_display_state_curr_cb(gconstpointer data)
             evin_input_grab_set_touching(&evin_ts_grab_state, true);
             evin_input_grab_set_touching(&evin_ts_grab_state, false);
         }
+        /* Fall through */
 
     case MCE_DISPLAY_ON:
     case MCE_DISPLAY_DIM: