Add a "pwd" utility to userland.

It's implemented as a separate process. How cute is that.
Tasks now have a current working directory. Spawned tasks inherit their
parent task's working directory.
Currently everyone just uses "/" as there's no way to chdir().

Userland/.gitignore

@@ -2,4 +2,5 @@ id
 sh
 ps
 ls
+pwd
 *.o

Userland/Makefile

@@ -2,13 +2,15 @@ OBJS = \
        id.o \
        sh.o \
        ps.o \
-       ls.o
+       ls.o \
+       pwd.o
 
 APPS = \
        id \
        sh \
        ps \
-       ls
+       ls \
+       pwd
 
 ARCH_FLAGS =
 STANDARD_FLAGS = -std=c++17 -nostdinc++ -nostdlib
@@ -40,6 +42,9 @@ ps: ps.o
 ls: ls.o
 	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
 
+pwd: pwd.o
+	$(LD) -o $@ $(LDFLAGS) $< ../LibC/LibC.a
+
 .cpp.o:
 	@echo "CXX $<"; $(CXX) $(CXXFLAGS) -o $@ -c $<
 

Userland/pwd.cpp

@@ -0,0 +1,15 @@
+#include <LibC/unistd.h>
+#include <LibC/stdio.h>
+
+int main(int c, char** v)
+{
+    char buffer[1024];
+    char* ptr = getcwd(buffer, sizeof(buffer));
+    if (!ptr) {
+        printf("getcwd() failed\n");
+        return 1;
+    }
+    printf("%s\n", ptr);
+    return 0;
+}
+