kernel: Activate FORTIFY_SOURCE for MIPS kernel 5.4

CONFIG_FORTIFY_SOURCE=y is already set in the generic kernel
configuration, but it is not working for MIPS on kernel 5.4, support for
MIPS was only added with kernel 5.5, other architectures like aarch64
support FORTIFY_SOURCE already since some time.

This patch adds support for FORTIFY_SOURCE to MIPS with kernel 5.4,
kernel 5.10 already supports this and needs no changes.

This backports one patch from kernel 5.5 and one fix from 5.8 to make
fortify source also work on our kernel 5.4.

The changes are not compatible with the
306-mips_mem_functions_performance.patch patch which was also removed
with kernel 5.10, probably because of the same problems. I think it is
not needed anyway as the compiler should automatically optimize the
calls to memset(), memcpy() and memmove() even when not explicitly
telling the compiler to use the build in variant.

This increases the size of an uncompressed kernel by less than 1 KB.

Acked-by: Rosen Penev <rosenp@gmail.com>
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>

target/linux/generic/pending-5.4/300-mips_expose_boot_raw.patch

@@ -9,7 +9,7 @@ Acked-by: Rob Landley <rob@landley.net>
 ---
 --- a/arch/mips/Kconfig
 +++ b/arch/mips/Kconfig
-@@ -1068,9 +1068,6 @@ config FW_ARC
+@@ -1069,9 +1069,6 @@ config FW_ARC
  config ARCH_MAY_HAVE_PC_FDC
  	bool
  
@@ -19,7 +19,7 @@ Acked-by: Rob Landley <rob@landley.net>
  config CEVT_BCM1480
  	bool
  
-@@ -3043,6 +3040,18 @@ choice
+@@ -3044,6 +3041,18 @@ choice
  		bool "Extend builtin kernel arguments with bootloader arguments"
  endchoice