-O2 for Pico2 builds, -O3 shows a GCC error

When -O3 is used to build LWIP, GCC emits a bogus error while compiling
DHCP.C:
>  ../dhcp.c:1453:30: error: writing 1 byte into a region of size 0

DHCP_OPTIONS_LEN was verified as being DHCP_MIN_OPTIONS_LEN (68U) and not
0 using #ifs and #errors in the dhcp.h header, but GCC somehow forgets
this while doing it's checks on O3.  Looks to be a bug in GCC to me,
so drop to -O2 for RP204 builds.

Author: earlephilhower

tests/build-rp2350.sh

@@ -15,7 +15,7 @@ elif [ "$BUILD_PARITY" = "odd" ]; then
     rem=1
 fi
 
-export FQBN=pico:rp2040:rpipico2:flash=4194304_0,arch=arm,freq=150,opt=Optimize3,rtti=Disabled,stackprotect=Disabled,exceptions=Disabled,dbgport=Disabled,dbglvl=None,usbstack=picosdk,ipbtstack=ipv4only,uploadmethod=default
+export FQBN=pico:rp2040:rpipico2:flash=4194304_0,arch=arm,freq=150,opt=Optimize2,rtti=Disabled,stackprotect=Disabled,exceptions=Disabled,dbgport=Disabled,dbglvl=None,usbstack=picosdk,ipbtstack=ipv4only,uploadmethod=default
 export PICO_BOARD=rp2350
 
 install_arduino nodebug