build: slightly change files to pass compilation

Compiled using Clang and encountered errors on ambiguous pointer
type, implicit conversion NULL to bool, and unused function, etc.
As a fix, this patch slightly updates the related codes.

Change-Id: I4a73d66293313dda36749036f5c73aaf2a445231

test/tool/tool.cpp

@@ -139,7 +139,6 @@ bool is_trace_local = true;
 // SPM trace enabled
 bool is_spm_trace = false;
 
-static inline uint32_t GetPid() { return syscall(__NR_getpid); }
 static inline uint32_t GetTid() { return syscall(__NR_gettid); }
 
 // Error handler