[lldb] Add -Wl,-rpath to make tests run with fresh built libc++

On my Debian machine, system libc++/libc++abi is not installed (`libc++1-9 libc++abi-9`),
21 check-lldb-api tests fail because -stdlib=libc++ linked executables cannot
find runtime libc++.so.1 at runtime.

Use the `-Wl,-rpath,$(LLVM_LIBS_DIR)` mechanism in
`packages/Python/lldbsuite/test/make/Makefile.rules` (D58630 for NetBSD) to
allow such tests compile/link with fresh libc++ built beside lldb.
(A system libc++.so.1 is not guaranteed to match fresh libc++ header files.)

Some tweaks to the existing NetBSD rule when generalizing:

* Drop `-L$(LLVM_LIBS_DIR)` since Clang driver adds it correctly.
* Add `-stdlib=libc++` only for `USE_LIBCPP`.

Also, drop `-isystem /usr/include/c++/v1` introduced in D9426. It is not needed
by Clang driver. GCC using libc++ requires more setup.

I don't find any test needing `-Wl,-rpath` in `test/Shell/helper/{build,toolchain}.py` (D58630 for NetBSD added them).

Reviewed By: labath

Differential Revision: https://reviews.llvm.org/D94888

Author: MaskRay

lldb/packages/Python/lldbsuite/test/dotest.py

@@ -761,8 +761,6 @@ def canRunLibcxxTests():
         return True, "libc++ always present"
 
     if platform == "linux":
-        if os.path.isdir("/usr/include/c++/v1"):
-            return True, "Headers found, let's hope they work"
         with tempfile.NamedTemporaryFile() as f:
             cmd = [configuration.compiler, "-xc++", "-stdlib=libc++", "-o", f.name, "-"]
             p = subprocess.Popen(cmd, stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True)

lldb/packages/Python/lldbsuite/test/make/Makefile.rules

@@ -279,11 +279,6 @@ CXXFLAGS += -std=c++11 $(CFLAGS) $(ARCH_CXXFLAGS) $(CXXFLAGS_EXTRAS)
 LD = $(CC)
 LDFLAGS ?= $(CFLAGS)
 LDFLAGS += $(LD_EXTRAS) $(ARCH_LDFLAGS)
-ifneq (,$(LLVM_LIBS_DIR))
-	ifeq ($(OS),NetBSD)
-		LDFLAGS += -L$(LLVM_LIBS_DIR) -Wl,-rpath,$(LLVM_LIBS_DIR)
-	endif
-endif
 ifeq (,$(filter $(OS), Windows_NT Android Darwin))
 	ifneq (,$(filter YES,$(ENABLE_THREADS)))
 		LDFLAGS += -pthread
@@ -393,21 +388,18 @@ endif
 
 ifeq (1,$(USE_LIBCPP))
 	CXXFLAGS += -DLLDB_USING_LIBCPP
-	ifeq "$(OS)" "Linux"
-		ifneq (,$(findstring clang,$(CC)))
-			CXXFLAGS += -stdlib=libc++
-			LDFLAGS += -stdlib=libc++
-		else
-			CXXFLAGS += -isystem /usr/include/c++/v1
-			LDFLAGS += -lc++
-		endif
-	else ifeq "$(OS)" "Android"
+	ifeq "$(OS)" "Android"
 		# Nothing to do, this is already handled in
 		# Android.rules.
 	else
 		CXXFLAGS += -stdlib=libc++
 		LDFLAGS += -stdlib=libc++
 	endif
+	ifneq (,$(filter $(OS), FreeBSD Linux NetBSD))
+		ifneq (,$(LLVM_LIBS_DIR))
+			LDFLAGS += -Wl,-rpath,$(LLVM_LIBS_DIR)
+		endif
+	endif
 endif
 
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