awk: fix detection of VAR=VAL arguments

1NAME=VAL is not it, neither is VA.R=VAL

function                                             old     new   delta
next_input_file                                      216     214      -2
is_assignment                                        115      91     -24
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(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-26)             Total: -26 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
1 file changed