helper: add compiler.h to handle compiler specific workarounds

Not all compilers nor compiler versions supports the attributes
used in OpenOCD code.
Collect in a single file the workaround to handle them.

Change-Id: I92d871337281169134ce8e40b2064591518be71f
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7519
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/helper/Makefile.am

@@ -34,7 +34,8 @@ noinst_LTLIBRARIES += %D%/libhelper.la
 	%D%/jep106.h \
 	%D%/jep106.inc \
 	%D%/jim-nvp.h \
-	%D%/nvp.h
+	%D%/nvp.h \
+	%D%/compiler.h
 
 STARTUP_TCL_SRCS += %D%/startup.tcl
 EXTRA_DIST += \