Fix RawSerial when used with ARMCC microlib
Fix RawSerial when used with ARMCC microlib

The function vsnprintf does not properly handle a size of zero for
the destination buffer, and will write data to it.  If the buffer is
set to null this will cause a hardfault.  This patch adds a workaround
for this bug by using a buffer of size 1.

maximmbed/mbed,mbedmicro/mbed,kl-cruz/mbed-os,kjbracey-arm/mbed,j-greffe/mbed-os,tung7970/mbed-os,mmorenobarm/mbed-os,netzimme/mbed-os,nRFMesh/mbed-os,bikeNomad/mbed,fahhem/mbed-os,betzw/mbed-os,mmorenobarm/mbed-os,fanghuaqi/mbed,radhika-raghavendran/mbed-os5.1-onsemi,ryankurte/mbed-os,CalSol/mbed,kl-cruz/mbed-os,jeremybrodt/mbed,mazimkhan/mbed-os,geky/mbed,YarivCol/mbed-os,DanKupiniak/mbed,dbestm/mbed,mbedmicro/mbed,nRFMesh/mbed-os,bikeNomad/mbed,j-greffe/mbed-os,nvlsianpu/mbed,andcor02/mbed-os,c1728p9/mbed-os,infinnovation/mbed-os,adamgreen/mbed,c1728p9/mbed-os,arostm/mbed-os,cvtsi2sd/mbed-os,maximmbed/mbed,bulislaw/mbed-os,rgrover/mbed,dbestm/mbed,adustm/mbed,netzimme/mbed-os,nvlsianpu/mbed,monkiineko/mbed-os,rgrover/mbed,tung7970/mbed-os-1,betzw/mbed-os,mikaleppanen/mbed-os,YarivCol/mbed-os,adustm/mbed,fvincenzo/mbed-os,svogl/mbed-os,theotherjimmy/mbed,catiedev/mbed-os,c1728p9/mbed-os,mazimkhan/mbed-os,dbestm/mbed,catiedev/mbed-os,bcostm/mbed-os,andcor02/mbed-os,bulislaw/mbed-os,mbedmicro/mbed,andreaslarssonublox/mbed,j-greffe/mbed-os,RonEld/mbed,pradeep-gr/mbed-os5-onsemi,j-greffe/mbed-os,svastm/mbed,adamgreen/mbed,nvlsianpu/mbed,NXPmicro/mbed,YarivCol/mbed-os,HeadsUpDisplayInc/mbed,pradeep-gr/mbed-os5-onsemi,bcostm/mbed-os,svastm/mbed,kjbracey-arm/mbed,tung7970/mbed-os,RonEld/mbed,mazimkhan/mbed-os,nRFMesh/mbed-os,infinnovation/mbed-os,adustm/mbed,fvincenzo/mbed-os,arostm/mbed-os,RonEld/mbed,theotherjimmy/mbed,tung7970/mbed-os-1,ARM-software/mbed-beetle,jeremybrodt/mbed,screamerbg/mbed,CalSol/mbed,betzw/mbed-os,jeremybrodt/mbed,YarivCol/mbed-os,maximmbed/mbed,RonEld/mbed,pradeep-gr/mbed-os5-onsemi,theotherjimmy/mbed,Shengliang/mbed,geky/mbed,karsev/mbed-os,karsev/mbed-os,mmorenobarm/mbed-os,ryankurte/mbed-os,betzw/mbed-os,RonEld/mbed,jeremybrodt/mbed,monkiineko/mbed-os,pradeep-gr/mbed-os5-onsemi,adamgreen/mbed,bikeNomad/mbed,catiedev/mbed-os,adustm/mbed,NXPmicro/mbed,screamerbg/mbed,tung7970/mbed-os,geky/mbed,HeadsUpDisplayInc/mbed,ARM-software/mbed-beetle,fanghuaqi/mbed,radhika-raghavendran/mbed-os5.1-onsemi,mmorenobarm/mbed-os,fanghuaqi/mbed,theotherjimmy/mbed,kl-cruz/mbed-os,ryankurte/mbed-os,DanKupiniak/mbed,bikeNomad/mbed,nRFMesh/mbed-os,fanghuaqi/mbed,monkiineko/mbed-os,jrjang/mbed,radhika-raghavendran/mbed-os5.1-onsemi,svastm/mbed,theotherjimmy/mbed,netzimme/mbed-os,adustm/mbed,geky/mbed,NXPmicro/mbed,svogl/mbed-os,jrjang/mbed,andreaslarssonublox/mbed,DanKupiniak/mbed,fvincenzo/mbed-os,monkiineko/mbed-os,nvlsianpu/mbed,mbedmicro/mbed,infinnovation/mbed-os,mazimkhan/mbed-os,adustm/mbed,andcor02/mbed-os,bcostm/mbed-os,karsev/mbed-os,adamgreen/mbed,fahhem/mbed-os,mazimkhan/mbed-os,jeremybrodt/mbed,CalSol/mbed,nvlsianpu/mbed,dbestm/mbed,c1728p9/mbed-os,arostm/mbed-os,andcor02/mbed-os,jrjang/mbed,Archcady/mbed-os,theotherjimmy/mbed,HeadsUpDisplayInc/mbed,CalSol/mbed,arostm/mbed-os,maximmbed/mbed,jrjang/mbed,cvtsi2sd/mbed-os,kl-cruz/mbed-os,screamerbg/mbed,netzimme/mbed-os,rgrover/mbed,NXPmicro/mbed,HeadsUpDisplayInc/mbed,infinnovation/mbed-os,pradeep-gr/mbed-os5-onsemi,kl-cruz/mbed-os,mikaleppanen/mbed-os,Shengliang/mbed,j-greffe/mbed-os,Shengliang/mbed,infinnovation/mbed-os,cvtsi2sd/mbed-os,cvtsi2sd/mbed-os,Archcady/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,kjbracey-arm/mbed,infinnovation/mbed-os,geky/mbed,ARM-software/mbed-beetle,YarivCol/mbed-os,jrjang/mbed,bulislaw/mbed-os,betzw/mbed-os,HeadsUpDisplayInc/mbed,arostm/mbed-os,pradeep-gr/mbed-os5-onsemi,karsev/mbed-os,Archcady/mbed-os,j-greffe/mbed-os,karsev/mbed-os,Archcady/mbed-os,fahhem/mbed-os,bcostm/mbed-os,tung7970/mbed-os-1,YarivCol/mbed-os,CalSol/mbed,monkiineko/mbed-os,Shengliang/mbed,fvincenzo/mbed-os,betzw/mbed-os,catiedev/mbed-os,mazimkhan/mbed-os,DanKupiniak/mbed,jrjang/mbed,radhika-raghavendran/mbed-os5.1-onsemi,bikeNomad/mbed,ARM-software/mbed-beetle,rgrover/mbed,tung7970/mbed-os,andcor02/mbed-os,bulislaw/mbed-os,adamgreen/mbed,cvtsi2sd/mbed-os,mbedmicro/mbed,fvincenzo/mbed-os,catiedev/mbed-os,tung7970/mbed-os,fahhem/mbed-os,screamerbg/mbed,NXPmicro/mbed,karsev/mbed-os,ryankurte/mbed-os,bulislaw/mbed-os,HeadsUpDisplayInc/mbed,fanghuaqi/mbed,bcostm/mbed-os,mikaleppanen/mbed-os,bcostm/mbed-os,c1728p9/mbed-os,andreaslarssonublox/mbed,maximmbed/mbed,andreaslarssonublox/mbed,catiedev/mbed-os,arostm/mbed-os,monkiineko/mbed-os,nRFMesh/mbed-os,Shengliang/mbed,mmorenobarm/mbed-os,andcor02/mbed-os,CalSol/mbed,RonEld/mbed,rgrover/mbed,svastm/mbed,Shengliang/mbed,svogl/mbed-os,nRFMesh/mbed-os,nvlsianpu/mbed,c1728p9/mbed-os,screamerbg/mbed,Archcady/mbed-os,fahhem/mbed-os,netzimme/mbed-os,netzimme/mbed-os,mmorenobarm/mbed-os,fahhem/mbed-os,svastm/mbed,andreaslarssonublox/mbed,maximmbed/mbed,radhika-raghavendran/mbed-os5.1-onsemi,ryankurte/mbed-os,cvtsi2sd/mbed-os,dbestm/mbed,screamerbg/mbed,mikaleppanen/mbed-os,svogl/mbed-os,ryankurte/mbed-os,kjbracey-arm/mbed,NXPmicro/mbed,svogl/mbed-os,bulislaw/mbed-os,kl-cruz/mbed-os,tung7970/mbed-os-1,adamgreen/mbed,tung7970/mbed-os-1,Archcady/mbed-os,mikaleppanen/mbed-os,svogl/mbed-os,dbestm/mbed,mikaleppanen/mbed-os