LibC+userspace: Make everything compile with -Wall -Wextra -Werror

I added -Wall -Wextra -Werror as public compile flags to libc. Now
everything in userspace in compiled using these flags. I made all
necessary changes to allow compilation to work.

Only exception is execvp which has a large stack usage. Maybe it
should use malloc for the buffer but posix allows ENOMEM only when
kernel is out of memory... This can be fixed when fexecve is
implemented and there is no need for absolute path.

libc/CMakeLists.txt

@@ -47,6 +47,7 @@ add_library(libc ${LIBC_SOURCES})
 add_dependencies(libc headers crtx-install)
 
 target_compile_options(libc PRIVATE -g -Wstack-usage=512)
+target_compile_options(libc PUBLIC -Wall -Wextra -Werror -Wno-error=stack-usage=)
 
 add_custom_target(libc-install
 	COMMAND ${CMAKE_COMMAND} -E copy_if_different ${CMAKE_CURRENT_BINARY_DIR}/libc.a ${BANAN_LIB}/

libc/pwd.cpp

@@ -104,7 +104,7 @@ struct passwd* getpwnam(const char* name)
 {
 	passwd* pwd;
 	setpwent();
-	while (pwd = getpwent())
+	while ((pwd = getpwent()))
 		if (strcmp(pwd->pw_name, name) == 0)
 			return pwd;
 	return nullptr;
@@ -114,7 +114,7 @@ struct passwd* getpwuid(uid_t uid)
 {
 	passwd* pwd;
 	setpwent();
-	while (pwd = getpwent())
+	while ((pwd = getpwent()))
 		if (pwd->pw_uid == uid)
 			return pwd;
 	return nullptr;

libc/stdio.cpp

@@ -13,7 +13,7 @@ struct FILE
 	bool eof		{ false };
 	bool error		{ false };
 
-	unsigned char buffer[BUFSIZ];
+	unsigned char buffer[BUFSIZ] {};
 	uint32_t buffer_index { 0 };
 };
 
@@ -260,7 +260,7 @@ size_t fread(void* buffer, size_t size, size_t nitems, FILE* file)
 
 	while (nread < target)
 	{
-		size_t ret = syscall(SYS_READ, file->fd, (uint8_t*)buffer + nread, target - nread);
+		ssize_t ret = syscall(SYS_READ, file->fd, (uint8_t*)buffer + nread, target - nread);
 
 		if (ret < 0)
 			file->error = true;