New gcc breaks compilation of -Os programs that use problematic static functions

[CelesteBlue-dev]

Newer gcc (>8 maybe) uses different optimizations, which breaks compilation of some programs that have the -Os flag and use problematic static functions like memset.

Logs:

arm-vita-eabi-gcc -fPIE -fno-zero-initialized-in-bss -std=c99 -mcpu=cortex-a9 -Os -mthumb   -c -o payload.o payload.c
arm-vita-eabi-gcc -fPIE -fno-zero-initialized-in-bss -std=c99 -mcpu=cortex-a9 -Os -mthumb payload.o -o payload.elf -T linker.x -nostartfiles -nostdlib -pie
/usr/local/vitasdk/bin/../lib/gcc/arm-vita-eabi/10.3.0/../../../../arm-vita-eabi/bin/ld.exe: payload.o: in function `one':
payload.c:(.text+0xa34): undefined reference to `memset'
/usr/local/vitasdk/bin/../lib/gcc/arm-vita-eabi/10.3.0/../../../../arm-vita-eabi/bin/ld.exe: payload.o: in function `two':
payload.c:(.text+0x19b0): undefined reference to `memset'
/usr/local/vitasdk/bin/../lib/gcc/arm-vita-eabi/10.3.0/../../../../arm-vita-eabi/bin/ld.exe: payload.o: in function `three':
payload.c:(.text+0x1faa): undefined reference to `memset'
collect2.exe: error: ld returned 1 exit status

Known workarounds are:

1. Replace -Os with -O0. Compiles but produces a broken executable (kernel panic).
2. Search what optimizations are enabled on gcc10 for -Os that are not on gcc8, and disable them. Not tried.
3. Remove the static attribute of the problematic function. Produces a good executable but modifies output size because of more or less optimizations.
4. Add -fno-builtin flag but attribute(used) might be needed for those problematic static functions

This issue might have a common cause with issue #226.

A valid fix should be either a regression in gcc10 directly, or an automating of broken optimizations disabling.

[Princess-of-Sleeping]

This may not be a gcc break, A simple gcc loop optimization as it can be fixed by adding -fno-builtin as shown in workarounds 4.

gcc wants to use memset for code like

for(int i=0;i<0x2000;i++){
  array[i] = x;
}