[bug-diffutils] bug#70951: "make distcheck" regression due to DIFF_EXTERN

[Bruno Haible]

Hi,

My weekly diffutils continuous integration run fails at the "make distcheck"
step. The substep that fails is

$ make sc_tight_scope
tight_scope
brief
colors_style
context
curr
excluded
expand_tabs
file_label
files_can_be_treated_as_binary
function_regexp
group_format
horizon_lines
ignore_blank_lines
ignore_case
ignore_file_name_case
ignore_regexp
ignore_white_space
initial_tab
left_column
line_format
minimal
no_dereference_symlinks
no_diff_means_no_output
noparent
outfile
output_style
paginate
presume_output_tty
proc_dev
sdiff_column2_offset
sdiff_half_width
sdiff_merge_assist
speed_large_files
starting_file
strip_trailing_cr
suppress_blank_empty
suppress_common_lines
switch_string
tabsize
text
time_format
the above variables should have static scope
make[1]: *** [/DIFFUTILS/diffutils/build/tight-scope.mk:42: _gl_tight_scope] 
Error 1
make: *** [../maint.mk:1818: sc_tight_scope] Error 1

This is seen with various gcc versions (11, 13, 14).

To me, it looks like a regression in commit 
cceca01aba9399769b80348d60fbef00f429bd99,
related to the DIFF_EXTERN macro.

Bruno