Switch fs_mgr/*.c to C++.

This is the minimal change just to keep it building, and doesn't
attempt to clean up the code.

Bug: 34336098
Test: check device can boot

Change-Id: I5ff897874f1f14a9a5d1f14fedf1b0749e86dbb3
diff --git a/fs_mgr/Android.mk b/fs_mgr/Android.mk
index e321c17..956c702 100644
--- a/fs_mgr/Android.mk
+++ b/fs_mgr/Android.mk
@@ -18,11 +18,11 @@
 LOCAL_CLANG := true
 LOCAL_SANITIZE := integer
 LOCAL_SRC_FILES:= \
-    fs_mgr.c \
+    fs_mgr.cpp \
     fs_mgr_dm_ioctl.cpp \
-    fs_mgr_format.c \
-    fs_mgr_fstab.c \
-    fs_mgr_slotselect.c \
+    fs_mgr_format.cpp \
+    fs_mgr_fstab.cpp \
+    fs_mgr_slotselect.cpp \
     fs_mgr_verity.cpp \
     fs_mgr_avb.cpp \
     fs_mgr_avb_ops.cpp
@@ -48,7 +48,7 @@
 include $(CLEAR_VARS)
 LOCAL_CLANG := true
 LOCAL_SANITIZE := integer
-LOCAL_SRC_FILES:= fs_mgr_main.c
+LOCAL_SRC_FILES:= fs_mgr_main.cpp
 LOCAL_C_INCLUDES := $(LOCAL_PATH)/include
 LOCAL_MODULE:= fs_mgr
 LOCAL_MODULE_TAGS := optional