[libc] Add stubbed-out stdio and libdl functions

In order to fix link errors with libunwind, stub out these functions for
now.

src/libraries/libc/arch/amd64/crt/libdl.cpp

@@ -0,0 +1,7 @@
+
+extern "C" {
+    // Stub out these libdl functions for libunwind until
+    // we have a real libdl
+    int dladdr(const void *, void *) { return 0; }
+    int dl_iterate_phdr(void *, void *) { return 0; }
+}

src/libraries/libc/stdio.h

@@ -36,6 +36,10 @@ typedef size_t fpos_t;
 #define SEEK_END 1
 #define SEEK_SET 2
 
+extern FILE *stdin;
+extern FILE *stdout;
+extern FILE *stderr;
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -112,6 +116,10 @@ int feof(FILE *stream);
 int ferror(FILE *stream);
 void perror(const char *s);
 
+// Environment functions
+//
+char * getenv(const char *name);
+
 #ifdef __cplusplus
 } // extern "C"
 #endif

src/libraries/libc/stdio/fflush.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int fflush(FILE *stream) { return 0; }

src/libraries/libc/stdio/fprintf.cpp

@@ -0,0 +1,4 @@
+#include <stdio.h>
+
+int fprintf(FILE * restrict stream, const char * restrict format, ...) { return 0; }
+int vfprintf(FILE * restrict stream, const char * restrict format, va_list arg) { return 0; }

src/libraries/libc/stdio/fputc.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int fputc(char c, FILE *stream) { return 0; }

src/libraries/libc/stdio/fputs.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+int fputs(const char * restrict s, FILE * restrict stream) { return 0; }

src/libraries/libc/stdio/fwrite.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+size_t fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict stream) { return 0; }

src/libraries/libc/stdio/getenv.cpp

@@ -0,0 +1,3 @@
+#include <stdio.h>
+
+char * getenv(const char *name) { return nullptr; }

src/libraries/libc/stdio/stdio.cpp

@@ -0,0 +1,5 @@
+#include <stdio.h>
+
+FILE *stdin = nullptr;
+FILE *stdout = nullptr;
+FILE *stderr = nullptr;