runtime: add timespec definition for freebsd

R=golang-dev, devon.odell
CC=golang-dev
https://golang.org/cl/5340058

src/pkg/runtime/freebsd/386/defs.h

@@ -173,6 +173,12 @@ struct Ucontext {
 	byte pad_godefs_0[12];
 };
 
+typedef struct Timespec Timespec;
+struct Timespec {
+	int32 tv_sec;
+	int32 tv_nsec;
+};
+
 typedef struct Timeval Timeval;
 struct Timeval {
 	int32 tv_sec;

src/pkg/runtime/freebsd/amd64/defs.h

@@ -184,6 +184,12 @@ struct Ucontext {
 	byte pad_godefs_0[12];
 };
 
+typedef struct Timespec Timespec;
+struct Timespec {
+	int64 tv_sec;
+	int64 tv_nsec;
+};
+
 typedef struct Timeval Timeval;
 struct Timeval {
 	int64 tv_sec;

src/pkg/runtime/freebsd/defs.c

@@ -104,5 +104,7 @@ typedef siginfo_t $Siginfo;
 
 typedef mcontext_t $Mcontext;
 typedef ucontext_t $Ucontext;
+
+typedef struct timespec $Timespec;
 typedef struct timeval $Timeval;
 typedef struct itimerval $Itimerval;