[LINKER] Add single underscore to all definitions, no -D for dashed param.

This makes possibility for the script to append the definitions to CFLAGS
and LDFLAGS, and with the feature of disabling of -D prependation it will
make possible to generate ARCH_FLAGS generic to each specific chip.

ld/README

@@ -90,7 +90,10 @@ Line description:
           "+"   - Don't change the parent. Use for split long line to two.
 
   <data>: space-separated list of preprocessor symbols supplied to the linker.
-      -D option name is automatically prepended to each symbol definition
+      -D option name with single underscore is automatically prepended to each
+         symbol definition
+      if the symbol starts with dash "-", it is interpreted as parameter to
+      linker, and no -D or underscore is generated.
 
 All lines starting with # symbol are treated as Comments
 
@@ -118,14 +121,15 @@ Example:
 
 --- devices.data file ---
 stm32f05[01]?4* stm32f0 ROM=16K RAM=4K
-stm32f0 stm32 ROM_OFF=0x08000000 RAM_OFF=0x20000000
+stm32f0 stm32 ROM_OFF=0x08000000 RAM_OFF=0x20000000 -mcpu=cortex-m0 -mthumb
 stm32 END
 
 --- queried chip name ---
 stm32f051c4t6
 
 --- output of the awk script ---
--DROM=16K -DRAM=4K -DROM_OFF=0x08000000 -DRAM_OFF=0x20000000
+-D_ROM=16K -D_RAM=4K -D_ROM_OFF=0x08000000 -D_RAM_OFF=0x20000000 \
+-mcpu=cortex-m0 -mthumb
 
 The generated linker script file will contain sections rom and ram with 
 appropriate initialization code, specified in linker file source linker.ld.S