Rollup merge of rust-lang#81734 - richkadel:fixfordash, r=pnkfelix

Ensures `make` tests run under /bin/dash (if available), like CI, and fixes a Makefile

Note: This cherrypicks rust-lang#81688 (``@pnkfelix)``

Updates `tools.mk` to explicitly require `SHELL := /bin/dash`, since CI uses `dash` but other environments (including developer local machines) may default to `bash`.

Replaces bash-specific shell command in one Makefile with a dash-compatible alternative, and re-enables the affected Makefile test.

Removes apparently redundant definition of `UNAME`.

Also see: [zulip discussion thread](https://rust-lang.zulipchat.com/#narrow/stream/131828-t-compiler/topic/how.20to.20run.2Fbless.20src.2Ftest.2Frun-make-fulldeps.2Fcoverage.20.3F)

r? ``@pnkfelix``

FYI: ``@wesleywiser`` ``@tmandry``

src/test/run-make-fulldeps/coverage-reports/Makefile

@@ -1,4 +1,3 @@
-# ignore-test Broken; accidentally silently ignored on Linux CI; FIXME(#81688)
 # needs-profiler-support
 # ignore-windows-gnu
 # min-llvm-version: 11.0
@@ -128,7 +127,7 @@ endif
 			$$( \
 				for file in $(TMPDIR)/rustdoc-$@/*/rust_out; \
 				do \
-				[[ -x $$file ]] && printf "%s %s " -object $$file; \
+				[ -x "$$file" ] && printf "%s %s " -object $$file; \
 				done \
 			) \
 		2> "$(TMPDIR)"/[email protected] \

src/test/run-make-fulldeps/coverage/coverage_tools.mk

@@ -12,5 +12,3 @@
 # Enabling `-C link-dead-code` is not necessary when compiling with `-Z instrument-coverage`,
 # due to improvements in the coverage map generation, to add unreachable functions known to Rust.
 # Therefore, `-C link-dead-code` is no longer automatically enabled.
-
-UNAME = $(shell uname)

src/test/run-make-fulldeps/tools.mk

@@ -21,6 +21,19 @@ CGREP := "$(S)/src/etc/cat-and-grep.sh"
 # diff with common flags for multi-platform diffs against text output
 DIFF := diff -u --strip-trailing-cr
 
+# Some of the Rust CI platforms use `/bin/dash` to run `shell` script in
+# Makefiles. Other platforms, including many developer platforms, default to
+# `/bin/bash`. (In many cases, `make` is actually using `/bin/sh`, but `sh`
+# is configured to execute one or the other shell binary). `dash` features
+# support only a small subset of `bash` features, so `dash` can be thought of as
+# the lowest common denominator, and tests should be validated against `dash`
+# whenever possible. Most developer platforms include `/bin/dash`, but to ensure
+# tests still work when `/bin/dash`, if not available, this `SHELL` override is
+# conditional:
+ifneq (,$(wildcard /bin/dash))
+SHELL := /bin/dash
+endif
+
 # This is the name of the binary we will generate and run; use this
 # e.g. for `$(CC) -o $(RUN_BINFILE)`.
 RUN_BINFILE = $(TMPDIR)/$(1)