autoconf: Command-line Macros and whitespace

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1 12.15 Command-line Macros and whitespace
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1 Some `make' implementations may strip trailing whitespace off of macros
1 set on the command line in addition to leading whitespace.  Further,
1 some may strip leading whitespace off of macros set from environment
1 variables:
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1      $ echo 'print: ; @echo "x$(foo)x$(bar)x"' |
1        foo=' f f ' make -f - bar=' b b '
1      x f f xb b x  # AIX, BSD, GNU make
1      xf f xb b x   # HP-UX, IRIX, Tru64/OSF make
1      x f f xb bx   # Solaris make
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