Add support for using -g3 compiler option

Currently when one need to debug code with full
debugging symbols (including access to macros -g3) then
the linker fails because adding -g3 causes that preprocessed
{preprocld.filepath} file contains a series of #define like:

 #define __STDC__ 1
 #define __STDC_VERSION__ 201112L
 #define __STDC_UTF_16__ 1
 #define __STDC_UTF_32__ 1
 #define __STDC_HOSTED__ 1
 #define __GNUC__ 7
 #define __GNUC_MINOR__ 4
 #define __GNUC_PATCHLEVEL__ 0
 #define __VERSION__ "7.4.0"
 #define __ATOMIC_RELAXED 0
 #define __ATOMIC_SEQ_CST 5
 #define __ATOMIC_ACQUIRE 2
 #define __ATOMIC_RELEASE 3
 ...

which later on causes the linker to not accept such a file:

/usr/lib/gcc/arm-none-eabi/7.4.0/../../../../arm-none-eabi/bin/ld:/home/sw/Arduino/DS18B20Test/.build/preproc.ld:1: ignoring invalid character `#' in expression
/usr/lib/gcc/arm-none-eabi/7.4.0/../../../../arm-none-eabi/bin/ld:/home/sw/Arduino/DS18B20Test/.build/preproc.ld:1: syntax error

The fix removes entirely preprocessing of linker file operation step
and passes an appropriate value of the symbol directly to the linker
using: -Wl,--defsym= option.

Log excerpt:

Linking everything together...
"/usr/bin/arm-none-eabi-gcc" -mcpu=cortex-m3 -mthumb -Os --specs=nano.specs -Wl,--defsym=LD_MAX_SIZE=131072 -Wl,--defsym=LD_MAX_DATA_SIZE=20480

Signed-off-by: Damian Wrobel <[email protected]>

Author: dwrobel

platform.txt

@@ -37,7 +37,7 @@ compiler.cpp.flags={compiler.extra_flags} -c {build.flags.optimize} {compiler.wa
 
 compiler.ar.flags=rcs
 
-compiler.c.elf.flags=-mcpu={build.mcu} -mthumb {build.flags.optimize} {build.flags.ldspecs} -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--entry=Reset_Handler -Wl,--unresolved-symbols=report-all -Wl,--warn-common
+compiler.c.elf.flags=-mcpu={build.mcu} -mthumb {build.flags.optimize} {build.flags.ldspecs} -Wl,--defsym=LD_MAX_SIZE={upload.maximum_size} -Wl,--defsym=LD_MAX_DATA_SIZE={upload.maximum_data_size} -Wl,--cref -Wl,--check-sections -Wl,--gc-sections -Wl,--entry=Reset_Handler -Wl,--unresolved-symbols=report-all -Wl,--warn-common
 
 compiler.objcopy.eep.flags=-O ihex -j .eeprom --set-section-flags=.eeprom=alloc,load --no-change-warnings --change-section-lma .eeprom=0
 
@@ -94,12 +94,6 @@ recipe.hooks.prebuild.1.pattern.windows=cmd /c if not exist "{build.opt.sourcepa
 recipe.hooks.prebuild.1.pattern.linux=bash -c "[ -f {build.opt.sourcepath} ] || (mkdir -p {build.path}/sketch && touch {build.opt.path})"
 recipe.hooks.prebuild.1.pattern.macosx=bash -c "[ -f {build.opt.sourcepath} ] || (mkdir -p {build.path}/sketch && touch {build.opt.path})"
 
-# preprocess linker file
-preprocld.name=preproc.ld
-preprocld.filepath={build.path}/{preprocld.name}
-preprocld.flags=-DLD_MAX_SIZE={upload.maximum_size} -DLD_MAX_DATA_SIZE={upload.maximum_data_size}
-recipe.hooks.linking.prelink.1.pattern="{compiler.path}{compiler.c.cmd}" -x c -E -P {preprocld.flags} {compiler.c.flags} {build.info.flags} {compiler.c.extra_flags} {build.extra_flags} {compiler.arm.cmsis.c.flags} "{build.variant.path}/{build.ldscript}" -o "{preprocld.filepath}"
-
 # compile patterns
 # ---------------------
 
@@ -116,7 +110,7 @@ recipe.S.o.pattern="{compiler.path}{compiler.S.cmd}" {compiler.S.flags} {build.i
 recipe.ar.pattern="{compiler.path}{compiler.ar.cmd}" {compiler.ar.flags} {compiler.ar.extra_flags} "{archive_file_path}" "{object_file}"
 
 ## Combine gc-sections, archives, and objects
-recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} "-T{preprocld.filepath}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} {compiler.ldflags} {compiler.arm.cmsis.ldflags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -Wl,--start-group {object_files} -Wl,--whole-archive "{archive_file_path}" -Wl,--no-whole-archive -lc -Wl,--end-group -lm -lgcc -lstdc++
+recipe.c.combine.pattern="{compiler.path}{compiler.c.elf.cmd}" {compiler.c.elf.flags} "-T{build.variant.path}/{build.ldscript}" "-Wl,-Map,{build.path}/{build.project_name}.map" {compiler.c.elf.extra_flags} {compiler.ldflags} {compiler.arm.cmsis.ldflags} -o "{build.path}/{build.project_name}.elf" "-L{build.path}" -Wl,--start-group {object_files} -Wl,--whole-archive "{archive_file_path}" -Wl,--no-whole-archive -lc -Wl,--end-group -lm -lgcc -lstdc++
 
 ## Create output (.bin file)
 recipe.objcopy.bin.pattern="{compiler.path}{compiler.objcopy.cmd}" {compiler.elf2bin.flags} {compiler.elf2bin.extra_flags} "{build.path}/{build.project_name}.elf" "{build.path}/{build.project_name}.bin"