ld: preserve symbol sizes during data layout

Fixes the broken linux/amd64 build.
The symbol table, itself a symbol, was having
its size rounded up to the nearest word boundary.
If the rounding add >7 zero bytes then it confused
the debug/gosym symbol table parser.  So you've
got a 1/8 chance to hit the bug on an amd64 system.

Just started in the recent change because I fixed
the rounding to round to word boundary instead
of to 4-byte boundary.

R=r
CC=golang-dev
https://golang.org/cl/4241056

src/cmd/ld/data.c

@@ -788,7 +788,6 @@ dodata(void)
 	for(; s != nil && s->type < SDATA; s = s->next) {
 		s->type = SRODATA;
 		t = rnd(s->size, PtrSize);
-		s->size = t;
 		s->value = datsize;
 		datsize += t;
 	}
@@ -835,7 +834,6 @@ dodata(void)
 			datsize = rnd(datsize, 4);
 		else
 			datsize = rnd(datsize, 8);
-		s->size = t;
 		s->value = datsize;
 		datsize += t;
 	}