unistd: add getcwd

Signed-off-by: Simon Rozman <simon@rozman.si>

Tests/Tests.mm

@@ -5,6 +5,7 @@
 
 #import <XCTest/XCTest.h>
 #include "../include/MacStd/dyld.hpp"
+#include "../include/MacStd/unistd.hpp"
 
 @interface Tests : XCTestCase
 @end
@@ -24,6 +25,11 @@
 	XCTAssert(_NSGetExecutablePath(path) == 0);
 }
 
+- (void)test_getcwd {
+	std::string path;
+	XCTAssert(getcwd(path));
+}
+
 - (void)testPerformanceExample {
 	// This is an example of a performance test case.
 	[self measureBlock:^{