[regression] make 4.0+ breaks 'export' when '-e' option is given

[Enrico Scholz]

Hello,

to pass down *all* environment variables given on cmdline to sub-makes,
I used to write

| export ${MAKEOVERRIDES}

Unfortunately, this seems to be broken beginning with make 4.0 when '-e'
is specified:

--- /tmp/x.mk ---
FOO = bar
export ${MAKEOVERRIDES}

a:
        ${MAKE} -f ${firstword ${MAKEFILE_LIST}} b

b:
        @echo TEST1 '>${a-b}<'
        @echo TEST2 '>${a_b}<'
----

## working make
$ make -v
GNU Make 3.82

## working 'make' without '-e'
$ env -i PATH=/usr/bin:/bin make -f /tmp/x.mk -s \
      a-b='ok ab $(FOO) a-b=XXX' \
      a_b='ok ab ${FOO} a_b=XXX'
TEST1 >ok ab bar a-b=XXX<
TEST2 >ok ab bar a_b=XXX<

## working 'make' with '-e'
$ env -i PATH=/usr/bin:/bin make -f /tmp/x.mk -s -e \
      a-b='ok ab $(FOO) a-b=XXX' \
      a_b='ok ab ${FOO} a_b=XXX'
TEST1 >ok ab bar a-b=XXX<
TEST2 >ok ab bar a_b=XXX<

----

## broken make
$ ./make -v
GNU Make 4.1

## broken 'make' without '-e'; result ok
$ env -i PATH=/usr/bin:/bin ./make -f /tmp/x.mk -s \
      a-b='ok ab $(FOO) a-b=XXX' \
      a_b='ok ab ${FOO} a_b=XXX'
TEST1 >ok ab bar a-b=XXX<
TEST2 >ok ab bar a_b=XXX<

## broken 'make' with '-e'; result bad
$ env -i PATH=/usr/bin:/bin ./make -f /tmp/x.mk -s -e \
      a-b='ok ab $(FOO) a-b=XXX' \
      a_b='ok ab ${FOO} a_b=XXX'
TEST1 >XXX=<
TEST2 >XXX=<

----



Enrico