[Bug libstdc++/109814] [13/14 Regression] freestanding using cmath does not compile anymore

["lestofante88 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109814

--- Comment #5 from lesto fante <lestofante88 at gmail dot com> ---
> Presumably you're using newlib to provide the libm functions that <cmath> declares?

newlib-nano, trough the "-specs=nano.specs". 
Removing -ffreestanding in my project caused a decrease(!) in code size (42008
vs 41328), but an increase of max function stack usage (better inlining?)


> If people are using more than just <cmath> with -ffreestanding then things get harder

I personally like this breakage, i would have never known this build script had
this error if i would have never used with this compiler version, so big plus
for me.
Maybe a warning instead of an error?

I looked a bit online and it seems to be relatively common, considering how
hard can be finding stuff about linking in embedded.
Even ST's IDE * seems to be doing it, and if this is default, that means a lot
of people like me are just using forbitten lib in freestanding without
realizing :(

(*
https://community.st.com/s/question/0D50X0000AkShGlSQK/cannot-compile-release-configuration-no-rule-to-make-syscallso)

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arm-none-eabi-gcc -v
Using built-in specs.
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Target: arm-none-eabi
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Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 13.1.0 (Arch Repository)

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arm-none-eabi-gcc -v
Using built-in specs.
COLLECT_GCC=arm-none-eabi-gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/arm-none-eabi/12.2.0/lto-wrapper
Target: arm-none-eabi
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Thread model: single
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.0 (Arch Repository)

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arm-none-eabi-g++ -v                    
Using built-in specs.
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gcc version 8.2.1 20181213 (release) [gcc-8-branch revision 267074] (GNU Tools
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