[runtimes] Support ELF dependent libraries feature

As of r360984, LLD supports dependent libraries feature for ELF.
libunwind, libc++abi and libc++ have library dependencies: libdl librt
and libpthread, which means that when libunwind and libc++ are being
statically linked (using -static-libstdc++ flag), user has to manually
specify -ldl -lpthread which is onerous.

This change includes the lib pragma to specify the library dependencies
directly in the source that uses those libraries. This doesn't make any
difference when using linkers that don't support dependent libraries.
However, when using LLD that has dependent libraries feature, users no
longer have to manually specifying library dependencies when using
static linking, linker will pick the library automatically.

Differential Revision: https://reviews.llvm.org/D62090

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@362048 91177308-0d34-0410-b5e6-96231b3b80d8

src/algorithm.cpp

@@ -8,7 +8,12 @@
 
 #include "algorithm"
 #include "random"
+#ifndef _LIBCPP_HAS_NO_THREADS
 #include "mutex"
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 

src/chrono.cpp

@@ -37,6 +37,10 @@
 #endif
 #endif
 
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "rt")
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 namespace chrono

src/condition_variable.cpp

@@ -15,6 +15,10 @@
 #include "system_error"
 #include "__undef_macros"
 
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 condition_variable::~condition_variable()

src/debug.cpp

@@ -13,7 +13,12 @@
 #include "string"
 #include "cstdio"
 #include "__hash_table"
+#ifndef _LIBCPP_HAS_NO_THREADS
 #include "mutex"
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 

src/experimental/memory_resource.cpp

@@ -12,6 +12,9 @@
 #include "atomic"
 #elif !defined(_LIBCPP_HAS_NO_THREADS)
 #include "mutex"
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_LFTS_PMR

src/filesystem/operations.cpp

@@ -44,6 +44,10 @@
 #include <sys/time.h> // for gettimeofday and timeval
 #endif                // !defined(CLOCK_REALTIME)
 
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "rt")
+#endif
+
 #if defined(_LIBCPP_COMPILER_GCC)
 #if _GNUC_VER < 500
 #pragma GCC diagnostic ignored "-Wmissing-field-initializers"

src/memory.cpp

@@ -10,6 +10,9 @@
 #ifndef _LIBCPP_HAS_NO_THREADS
 #include "mutex"
 #include "thread"
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
 #endif
 #include "include/atomic_support.h"
 

src/mutex.cpp

@@ -12,6 +12,12 @@
 #include "include/atomic_support.h"
 #include "__undef_macros"
 
+#ifndef _LIBCPP_HAS_NO_THREADS
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 #ifndef _LIBCPP_HAS_NO_THREADS
 

src/shared_mutex.cpp

@@ -10,6 +10,9 @@
 #ifndef _LIBCPP_HAS_NO_THREADS
 
 #include "shared_mutex"
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 

src/thread.cpp

@@ -35,6 +35,10 @@
 #include <windows.h>
 #endif
 
+#if defined(__unix__) &&  defined(__ELF__) && defined(__clang__)
+#pragma comment(lib, "pthread")
+#endif
+
 _LIBCPP_BEGIN_NAMESPACE_STD
 
 thread::~thread()