[profile][Fuchsia] Add missing system header #include

The _zx_vmar_root_self function is not a system call but
a libc function declared in a separate header.

Reviewed By: gulfem

Differential Revision: https://reviews.llvm.org/D107616

Author: frobtech

compiler-rt/lib/profile/InstrProfilingUtil.c

@@ -34,6 +34,7 @@
 #endif
 
 #if defined(__Fuchsia__)
+#include <zircon/process.h>
 #include <zircon/syscalls.h>
 #endif