main/busybox: disable CONFIG_STATIC_LIBGCC for non-static builds

Previously, busybox linked statically against libgcc unconditionally
with release 1.33.0 this become configurable [1]. Linking dynamically
against libgcc should result in a size decrease.

[1]: https://git.busybox.net/busybox/commit/?id=39646dce329c1b88b1de8ef0c450813765fda202
7 jobs for !17345 with busybox-libgcc-dynamic in 2 minutes and 18 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Lint
failed #302587
docker-alpine x86_64 allowed to fail
lint

00:00:10

 
  Build
passed #302592
docker-alpine ci-build aarch64
build-aarch64

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passed #302593
docker-alpine ci-build armv7
build-armv7

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passed #302591
docker-alpine ci-build ppc64le
build-ppc64le

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passed #302590
docker-alpine ci-build s390x
build-s390x

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passed #302589
docker-alpine ci-build x86
build-x86

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passed #302588
docker-alpine ci-build x86_64
build-x86_64

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Name Stage Failure
failed
lint Lint
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