cmd/5l,cmd/8l: unbreak arm and 386 linkers

Add dragonflydynld to 5l and 8l so that they compile again.

R=golang-dev, bradfitz
CC=golang-dev
https://golang.org/cl/12739048

src/cmd/5l/asm.c

@@ -41,6 +41,7 @@ char linuxdynld[] = "/lib/ld-linux.so.3"; // 2 for OABI, 3 for EABI
 char freebsddynld[] = "/usr/libexec/ld-elf.so.1";
 char openbsddynld[] = "XXX";
 char netbsddynld[] = "/libexec/ld.elf_so";
+char dragonflydynld[] = "/libexec/ld-elf.so.2";
 
 int32
 entryvalue(void)

src/cmd/8l/asm.c

@@ -41,6 +41,7 @@ char linuxdynld[] = "/lib/ld-linux.so.2";
 char freebsddynld[] = "/usr/libexec/ld-elf.so.1";
 char openbsddynld[] = "/usr/libexec/ld.so";
 char netbsddynld[] = "/usr/libexec/ld.elf_so";
+char dragonflydynld[] = "/libexec/ld-elf.so.2";
 
 int32
 entryvalue(void)