ld: In map file use '=' in PROVIDE statements

ld: In map file use '=' in PROVIDE statements

Currently when recording a PROVIDE statement in a linker map file we
display something like:

    PROVIDE (SYMBOL, VALUE)

However, in a linker script we write these statements like this:

    PROVIDE (SYMBOL = VALUE);

This commit changes the output in the map file to be closer to linker
script format, the map file now contains:

    PROVIDE (SYMBOL = VALUE)

The ';' is still missing from the end, but map files are not intended
to be valid linker script input, so adding the ';' just seems like
clutter.

ld/ChangeLog:

	* ldexp.c (exp_print_tree): Use '=' instead of ',' when printing
	PROVIDE statements.
	* testsuite/ld-scripts/provide-4.map: Update expected output.
	* testsuite/ld-scripts/provide-5.map: Likewise.