ports: Always include debug information in the ELF.

For bare metal ARM & xtensa targets, passing -g will make the ELF file
larger but doesn't change the binary size.  However, this means tools like
gdb, addr2line, etc can extract source-level information from the ELF.

Also standardise -ggdb to -g, these produce the exact same ELF file on
arm-none-eabi-gcc and will use DWARF format for all these ports.

ports/minimal/Makefile

@@ -34,8 +34,9 @@ endif
 CSUPEROPT = -Os # save some code space
 
 # Tune for Debugging or Optimization
+CFLAGS += -g  # always include debug info in the ELF
 ifeq ($(DEBUG), 1)
-CFLAGS += -O0 -ggdb
+CFLAGS += -O0
 else
 CFLAGS += -Os -DNDEBUG
 CFLAGS += -fdata-sections -ffunction-sections