KCalc with the KDE libs, Qt, X, libc, and all of their dependencies would become far bigger than 10 MB.
This is not true in general.
For this code:
#include <stdio.h>
int main(void)
{
puts("hello world\n");
return 0;
}
By using -ffunction-sections -fdata-sections -Wl,--gc-sections (per https://news.ycombinator.com/item?id=19170667) I get this down to 804 KB. Still not quite what you suggest.
[1] Clang might just be using the same linker as GCC here, and you might blame including the extra stuff on the linker.
$ gcc -O3 foo.c -flto -static -o foo
$ du -sh foo
828K foo
$ strip foo
$ du -sh foo
760K foo
uClibc and musl libc have much better support for static linking, and you will be able to make a much smaller binary with them than you would static linking against glibc.
$ musl-gcc test.c -O2
$ ls -laB a.out
.rwxr-xr-x 15,776 roblabla 15 Feb 16:49 a.out
$ musl-gcc test.c -O2 -ffunction-sections -fdata-sections -Wl,--gc-sections -static
$ ls -laB a.out
.rwxr-xr-x 17,864 roblabla 15 Feb 16:48 a.out
It's true that without proper care, you might end up importing a whole lot of useless stuff though.
FWIW, I believe (but could very well be wrong) the reason that this works this well with MUSL is that every function is defined in its own translation unit. I doubt that Qt and KDE do that.