abseil-cpp: Add changes from openwrt PR #25802 #49

Job	Run time
Test Build / Test arm_cortex-a15_neon-vfpv4	4m 1s
Test Build / Test mipsel_24kc	3m 46s
Test Build / Test aarch64_generic	5m 28s
Test Build / Test mips_24kc	4m 53s
Test Build / Test powerpc_464fp	7m 2s
Test Build / Test i386_pentium-mmx	4m 58s
Test Build / Test powerpc_8548	3m 43s
Test Build / Test arm_cortex-a9_vfpv3-d16	3m 59s
Test Build / Test riscv64_generic	5m 37s
Test Build / Test x86_64	4m 15s
	47m 42s

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