Makefile: do not compile rust/download_web with old toolchain

libz-sys crate became incompatible with Alpine 3.13 toolchain (rust 1.47):

    error: unexpected token: `zng_prefix`
       --> /root/.cargo/registry/src/github.51.al-1ecc6299db9ec823/libz-sys-1.1.8/src/lib.rs:115:19
        |
    114 | extern "C" {
        |            - while parsing this item list starting here
    115 |     #[link_name = zng_prefix!(adler32)]
        |                   ^^^^^^^^^^
    ...
    241 | }
        | - the item list ends here

With Alpine 3.14 toolchain (rust 1.52):

    error[E0658]: arbitrary expressions in key-value attributes are unstable
       --> /root/.cargo/registry/src/github.51.al-1ecc6299db9ec823/libz-sys-1.1.8/src/lib.rs:115:19
        |
    115 |     #[link_name = zng_prefix!(adler32)]
        |                   ^^^^^^^^^^^^^^^^^^^^
        |
        = note: see issue #78835 <rust-lang/rust#78835> for more information

Makefile

@@ -99,12 +99,17 @@ else
 #   note: for more information, see https://github.com/rust-lang/rust/issues/62254
 # Old versions of rustc (<=1.44) fail to build socket2-0.4.0 because:
 #   error[E0658]: `match` is not allowed in a `const fn`
-#   Fnote: see issue #49146 <https://github.com/rust-lang/rust/issues/49146> for more information
+#   note: see issue #49146 <https://github.com/rust-lang/rust/issues/49146> for more information
 # Old versions of rustc (<=1.44) fail to build clap-2.33.3 because:
 #   error[E0723]: loops and conditional expressions are not stable in const fn
 #   note: for more information, see issue https://github.com/rust-lang/rust/issues/57563
 ifeq ($(call can-run,$(RUSTC) --version | grep '^rustc 1\.\(3[0-9]\|4[0-4]\)\.'),y)
 SUBDIRS_BLACKLIST += rust/asymkeyfind% rust/check_linux_pass% rust/download_web%
+else ifeq ($(call can-run,$(RUSTC) --version | grep '^rustc 1\.\(4[5-9]\|5[0-2]\)\.'),y)
+# Old versions of rustc (<=1.52) fail to build libz-sys-1.1.8 because:
+#   error[E0658]: arbitrary expressions in key-value attributes are unstable
+#   note: see issue #78835 <https://github.com/rust-lang/rust/issues/78835> for more information
+SUBDIRS_BLACKLIST += rust/download_web%
 endif
 endif
 

machines/Dockerfile-alpine3.13

@@ -52,7 +52,7 @@ COPY . /shared/
 CMD ["/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c: x86-read_64b_regs_in_32b_mode
 #       glossaries:

machines/Dockerfile-alpine3.14

@@ -51,7 +51,7 @@ COPY . /shared/
 CMD ["/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c: x86-read_64b_regs_in_32b_mode
 #       glossaries:

machines/Dockerfile-debian11-bullseye

@@ -62,7 +62,7 @@ COPY . /shared/
 CMD ["/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c:
 #       glossaries:
@@ -76,7 +76,7 @@ CMD ["/run_shared_test.sh"]
 #       rust:
 #       verification:
 #    With gcc -m32:
-#       Global blacklist: latex%
+#       Global blacklist: latex% rust/download_web%
 #       In sub-directories:
 #          c: gmp_functions gtk_alpha_window
 #          glossaries:

machines/Dockerfile-fedora31

@@ -65,7 +65,7 @@ COPY . /shared/
 CMD ["/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c:
 #       glossaries:
@@ -79,7 +79,7 @@ CMD ["/run_shared_test.sh"]
 #       rust:
 #       verification:
 #    With gcc -m32:
-#       Global blacklist: latex%
+#       Global blacklist: latex% rust/download_web%
 #       In sub-directories:
 #          c: gtk_alpha_window
 #          glossaries:

machines/Dockerfile-fedora32

@@ -65,7 +65,7 @@ COPY . /shared/
 CMD ["xvfb-run", "/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c:
 #       glossaries:
@@ -79,7 +79,7 @@ CMD ["xvfb-run", "/run_shared_test.sh"]
 #       rust:
 #       verification:
 #    With gcc -m32:
-#       Global blacklist: latex%
+#       Global blacklist: latex% rust/download_web%
 #       In sub-directories:
 #          c: gtk_alpha_window
 #          glossaries:

machines/Dockerfile-ubuntu1604-xenial

@@ -63,7 +63,7 @@ COPY . /shared/
 CMD ["/run_shared_test.sh"]
 
 # make list-nobuild:
-#    Global blacklist: latex%
+#    Global blacklist: latex% rust/download_web%
 #    In sub-directories:
 #       c:
 #       glossaries: check_sort_order.py
@@ -77,7 +77,7 @@ CMD ["/run_shared_test.sh"]
 #       rust:
 #       verification:
 #    With gcc -m32:
-#       Global blacklist: latex%
+#       Global blacklist: latex% rust/download_web%
 #       In sub-directories:
 #          c: gmp_functions gtk_alpha_window
 #          glossaries: check_sort_order.py