Makefile: make-4.3 now longer un-escapes \# in macros

make-4.3 shipped with a backward incompatible change in how sharp signs
are handled in macros. Previously, up to make 4.2, the sharp sign would
always start a comment, unless backslash-escaped, even in a macro or a
fucntion call.

Now, the sharp sign is no longer starting a comment when it appears
inside such a macro or function call. This behaviour was supposed to be
in force since 3.81, but was not; 4.3 fixed the code to match the doc.

As such, use of external toolchains is broken, as we use the sharp sign
in the copy_toolchain_sysroot macro, in shell variable expansion to
strip off any leading /: ${target\#/}.

Fix that by applying the workaround suggested in the release annoucement
[0], by using a variable to hold a sharp sign.

[0] https://lists.gnu.org/archive/html/info-gnu/2020-01/msg00004.html

Signed-off-by: Yaroslav Syrytsia <[email protected]>
[[email protected]:
  - move the SHARP_SIGN definition out of Makefile and into support/
  - expand the commit log
]
Signed-off-by: Yann E. MORIN <[email protected]>

support/misc/utils.mk

@@ -14,6 +14,20 @@ comma := ,
 empty :=
 space := $(empty) $(empty)
 
+# make 4.3:
+# https://lwn.net/Articles/810071/
+# Number signs (#) appearing inside a macro reference or function invocation
+# no longer introduce comments and should not be escaped with backslashes:
+# thus a call such as:
+# foo := $(shell echo '#')
+# is legal. Previously the number sign needed to be escaped, for example:
+# foo := $(shell echo '\#')
+# Now this latter will resolve to "\#". If you want to write makefiles
+# portable to both versions, assign the number sign to a variable:
+# H := \#
+# foo := $(shell echo '$H')
+SHARP_SIGN := \#
+
 # Case conversion macros. This is inspired by the 'up' macro from gmsl
 # (https://gmsl.sf.net). It is optimised very heavily because these macros
 # are used a lot. It is about 5 times faster than forking a shell and tr.

toolchain/helpers.mk

@@ -119,12 +119,12 @@ copy_toolchain_sysroot = \
  done ; \
  for link in $$(find $(STAGING_DIR) -type l); do \
  target=$$(readlink $${link}) ; \
- if [ "$${target}" == "$${target\#/}" ] ; then \
+ if [ "$${target}" == "$${target$(SHARP_SIGN)/}" ] ; then \
  continue ; \
  fi ; \
- relpath="$(call relpath_prefix,$${target\#/})" ; \
- echo "Fixing symlink $${link} from $${target} to $${relpath}$${target\#/}" ; \
- ln -sf $${relpath}$${target\#/} $${link} ; \
+ relpath="$(call relpath_prefix,$${target$(SHARP_SIGN)/})" ; \
+ echo "Fixing symlink $${link} from $${target} to $${relpath}$${target$(SHARP_SIGN)/}" ; \
+ ln -sf $${relpath}$${target$(SHARP_SIGN)/} $${link} ; \
  done ; \
  relpath="$(call relpath_prefix,$${ARCH_LIB_DIR})" ; \
  if [ "$${relpath}" != "" ]; then \