Stub out some glibc-specific functions

This allows support for alternative libcs like musl

--- tdesktop-3.5.2-full.orig/Telegram/lib_base/base/platform/linux/base_info_linux.cpp
+++ tdesktop-3.5.2-full/Telegram/lib_base/base/platform/linux/base_info_linux.cpp
@@ -22,7 +22,7 @@
 
 #include <sys/utsname.h>
 
-#ifdef Q_OS_LINUX
+#if defined(Q_OS_LINUX) && defined(__GLIBC__)
 #include <gnu/libc-version.h>
 #endif // Q_OS_LINUX
 
@@ -200,7 +200,7 @@
 }
 
 QString GetLibcName() {
-#ifdef Q_OS_LINUX
+#if defined(Q_OS_LINUX) && defined(__GLIBC__)
 	return "glibc";
 #endif // Q_OS_LINUX
 
@@ -208,7 +208,7 @@
 }
 
 QString GetLibcVersion() {
-#ifdef Q_OS_LINUX
+#if defined(Q_OS_LINUX) && defined(__GLIBC__)
 	static const auto result = [&] {
 		const auto version = QString::fromLatin1(gnu_get_libc_version());
 		return QVersionNumber::fromString(version).isNull() ? QString() : version;