[libc] Created syscall trampolines in libc

Using syscalls.inc (moved to src/include) generate trampoline functions
for directly calling syscalls with libc functions.

scripts/templates/build.ninja.j2

@@ -47,7 +47,8 @@ asflags = $
     -DVERSION_MAJOR={{ version_major }} $
     -DVERSION_MINOR={{ version_minor }} $
     -DVERSION_PATCH={{ version_patch }} $
-    -DVERSION_GITSHA=0x{{ version_sha }}
+    -DVERSION_GITSHA=0x{{ version_sha }} $
+    -I${srcroot}/src/include
 
 cflags = -std=c11
 cxxflags = -std=c++14