liblog: add -Wall,-Wextra and do related clean-up.

Test: build
Change-Id: I3b33f2b896cb8bf7ad9edf110d1739d559028282
diff --git a/liblog/logprint.cpp b/liblog/logprint.cpp
index 3a54445..939c1b3 100644
--- a/liblog/logprint.cpp
+++ b/liblog/logprint.cpp
@@ -291,8 +291,10 @@
   return 1;
 }
 
+#ifndef __MINGW32__
 static const char tz[] = "TZ";
 static const char utc[] = "UTC";
+#endif
 
 /**
  * Returns FORMAT_OFF on invalid string
@@ -1189,6 +1191,7 @@
   return p - begin;
 }
 
+#ifdef __ANDROID__
 static char* readSeconds(char* e, struct timespec* t) {
   unsigned long multiplier;
   char* p;
@@ -1229,7 +1232,6 @@
   return (long long)now->tv_sec * NS_PER_SEC + now->tv_nsec;
 }
 
-#ifdef __ANDROID__
 static void convertMonotonic(struct timespec* result, const AndroidLogEntry* entry) {
   struct listnode* node;
   struct conversionList {