Consistently use RUNPATH in our libraries

When loading dependencies on Linux, we can either use `RPATH` or
`RUNPATH` as a list of relative paths to search for libraries.  The
difference, for our purposes, mainly lies within how this interacts with
`LD_LIBRARY_PATH`: `RPATH` is searched first, then `LD_LIBRARY_PATH`,
then `RUNPATH`.  So by using `RUNPATH` here, we are explicitly allowing
ourselves to be overridden by `LD_LIBRARY_PATH`.  This is fine, as long
as we are consistent across our entire library line, however in the
`v1.8.0` release, there was an inconsistency, reported in [0].

The inconsistency occured because of the following confluence of factors:

 - Ancient `ld` builds (such as the one used in our build environment)
   do not default to using `RUNPATH`, but instead use `RPATH`.
 - `patchelf`, when it rewrites the RPATH, will default to using
   `RUNPATH` instead.
 - We were only using `patchelf` on `libjulia-internal`, not on
   `libjulia-codegen`, which was newly added in `v1.8`.

These three factors together caused us to ship a binary with `RUNPATH`
in `libjulia-internal`, but `RPATH` in `libjulia-codegen`, which caused
loading to fail in [0] due to first `libjulia-internal` being loaded,
(which brought in the external `libstdc++`), then `libjulia-codegen`
failed to load (because it found an incompatible `libstdc++`), causing
the mysterious compiler error.

This PR fixes this twofold; first, when building the libraries in the
first place, we pass `--enable-new-dtags` to the linker to encourage it
to use `runpath` when possible.  This removes the possibility for a
missing `patchelf` invocation to break things in this way.  Second, we
apply `patchelf` properly to `libjulia-codegen` as well.

[0] #46409

Make.inc

@@ -1223,6 +1223,9 @@ else
   NO_WHOLE_ARCHIVE := -Wl,--no-whole-archive
 endif
 
+# Initialize these once, then add to them in OS-specific blocks
+JLIBLDFLAGS :=
+
 ifeq ($(OS), Linux)
 OSLIBS += -Wl,--no-as-needed -ldl -lrt -lpthread -latomic -Wl,--export-dynamic,--as-needed,--no-whole-archive
 # Detect if ifunc is supported
@@ -1236,14 +1239,14 @@ ifneq ($(SANITIZE),1)
 JLDFLAGS += -Wl,-no-undefined
 endif
 ifeq (-Bsymbolic-functions, $(shell $(LD) --help | grep -o -e "-Bsymbolic-functions"))
-JLIBLDFLAGS := -Wl,-Bsymbolic-functions
-else
-JLIBLDFLAGS :=
+JLIBLDFLAGS += -Wl,-Bsymbolic-functions
 endif
+ifeq (--enable-new-dtags, $(shell $(LD) --help | grep -o -e "--enable-new-dtags"))
+JLIBLDFLAGS += -Wl,--enable-new-dtags 
+endif
+
 # Linker doesn't detect automatically that Julia doesn't need executable stack
 JLIBLDFLAGS += -Wl,-z,noexecstack
-else ifneq ($(OS), Darwin)
-JLIBLDFLAGS :=
 endif
 
 ifeq ($(OS), FreeBSD)
@@ -1266,7 +1269,7 @@ OSLIBS += -framework CoreFoundation
 WHOLE_ARCHIVE := -Xlinker -all_load
 NO_WHOLE_ARCHIVE :=
 HAVE_SSP := 1
-JLIBLDFLAGS := -Wl,-compatibility_version,$(SOMAJOR) -Wl,-current_version,$(JULIA_MAJOR_VERSION).$(JULIA_MINOR_VERSION).$(JULIA_PATCH_VERSION)
+JLIBLDFLAGS += -Wl,-compatibility_version,$(SOMAJOR) -Wl,-current_version,$(JULIA_MAJOR_VERSION).$(JULIA_MINOR_VERSION).$(JULIA_PATCH_VERSION)
 endif
 
 ifeq ($(OS), WINNT)

Makefile

@@ -370,8 +370,10 @@ endif
 ifneq (,$(findstring $(OS),Linux FreeBSD))
 ifeq ($(JULIA_BUILD_MODE),release)
 	$(PATCHELF) --set-rpath '$$ORIGIN:$$ORIGIN/$(reverse_private_libdir_rel)' $(DESTDIR)$(private_libdir)/libjulia-internal.$(SHLIB_EXT)
+	$(PATCHELF) --set-rpath '$$ORIGIN:$$ORIGIN/$(reverse_private_libdir_rel)' $(DESTDIR)$(private_libdir)/libjulia-codegen.$(SHLIB_EXT)
 else ifeq ($(JULIA_BUILD_MODE),debug)
 	$(PATCHELF) --set-rpath '$$ORIGIN:$$ORIGIN/$(reverse_private_libdir_rel)' $(DESTDIR)$(private_libdir)/libjulia-internal-debug.$(SHLIB_EXT)
+	$(PATCHELF) --set-rpath '$$ORIGIN:$$ORIGIN/$(reverse_private_libdir_rel)' $(DESTDIR)$(private_libdir)/libjulia-codegen-debug.$(SHLIB_EXT)
 endif
 endif