build, qt: backport patches

Summary:
This brings us to the same set of patches as the current tip of the Core repository, minus the ones for architectures we don't support (mainly android and arm64 MacOS)

build, qt: Hardcode last modified timestamp in Qt RCC

This change allows the already built qt package to be reused even with
the SOURCE_DATE_EPOCH variable set, e.g., for Guix builds.

build: patch around qt duplicate symbol issue

This is currently causing the same failure in two different PRs:

bash
duplicate symbol 'lcQpaFonts()' in:
    /tmp/cirrus-ci-build/depends/x86_64-apple-darwin/lib/libQt5ThemeSupport.a(qgenericunixthemes.o)
    /tmp/cirrus-ci-build/depends/x86_64-apple-darwin/lib/libQt5FontDatabaseSupport.a(qfontengine_coretext.o)
ld: 1 duplicate symbol for architecture x86_64

bash
x86_64-apple-darwin-ld: error: duplicate symbol: __Z10lcQpaFontsv
>>> defined in /tmp/cirrus-ci-build/depends/x86_64-apple-darwin/lib/libQt5ThemeSupport.a(qgenericunixthemes.o)
>>> defined in /tmp/cirrus-ci-build/depends/x86_64-apple-darwin/lib/libQt5FontDatabaseSupport.a(qfontengine_coretext.o)

Co-authored-by: Hennadii Stepanov <32963518+hebasto@users.noreply.github.com>

depends: modify FastFixedDtoa optimisation flags

This fixes a non-determinism issue in the asm produced for
this function when cross-compiling on x86_64 and aarch64 for
the arm-linux-gnueabihf HOST.

Related to #21194.

guix: More thoroughly control native toolchain

This patch has been updated (line numbers in the diff only) to account for a Qt version bump (D13918)

This is a backport of core#23862, core#24722 and core#25643

and https://github.com/bitcoin/bitcoin/pull/21375/commits/c1ae726a13ecfa5e7e9fdc3030a8110b8bb263f8

Depends on D13926

Test Plan: local crossbuild of qt, gitian builds, guix build

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13927