auto merge of #15006 : alexcrichton/rust/fix-nightly, r=brson

The nightly builds on linux have been failing over the past few days due to a
malformed LD_LIBRARY_PATH. It appears that the underlying cause is that one of
the tests, dep-info-custom, recursively invokes make but the RUSTC variable
passed down has the string "$LD_LIBRARY_PATH". This is intended to read the
host's original LD_LIBRARY_PATH, but it appears that the makefile is eagerly
expanding the "$L" to nothing, causing the original host's LD_LIBRARY_PATH to be
ignored.

This fix removes passing the string "$LD_LIBRARY_PATH" and rather expands it
eagerly to ensure that escaping doesn't happen at a later stage. I'm still not
entirely sure why the makefile is interpreting the dollar as a variable, but
this seems to fix the issue.

Author: bors

src/test/run-make/tools.mk

@@ -1,12 +1,9 @@
-export LD_LIBRARY_PATH:=$(TMPDIR):$(LD_LIBRARY_PATH)
-export DYLD_LIBRARY_PATH:=$(TMPDIR):$(DYLD_LIBRARY_PATH)
-
 # These deliberately use `=` and not `:=` so that client makefiles can
 # augment HOST_RPATH_DIR / TARGET_RPATH_DIR.
 HOST_RPATH_ENV = \
-    $(LD_LIB_PATH_ENVVAR)=$(HOST_RPATH_DIR):$$$(LD_LIB_PATH_ENVVAR)
+    $(LD_LIB_PATH_ENVVAR)="$(HOST_RPATH_DIR):$($(LD_LIB_PATH_ENVVAR))"
 TARGET_RPATH_ENV = \
-    $(LD_LIB_PATH_ENVVAR)=$(TARGET_RPATH_DIR):$$$(LD_LIB_PATH_ENVVAR)
+    $(LD_LIB_PATH_ENVVAR)="$(TARGET_RPATH_DIR):$($(LD_LIB_PATH_ENVVAR))"
 
 RUSTC := $(HOST_RPATH_ENV) $(RUSTC) --out-dir $(TMPDIR) -L $(TMPDIR)
 CC := $(CC) -L $(TMPDIR)
@@ -43,7 +40,6 @@ DYLIB_GLOB = $(1)*.dll
 DYLIB = $(TMPDIR)/$(1).dll
 BIN = $(1).exe
 RPATH_LINK_SEARCH =
-RUSTC := PATH="$(PATH):$(LD_LIBRARY_PATH)" $(RUSTC)
 else
 RUN = $(TARGET_RPATH_ENV) $(RUN_BINFILE)
 FAIL = $(TARGET_RPATH_ENV) $(RUN_BINFILE) && exit 1 || exit 0