Description of problem:
After upgrading glibc to version 2.31 clang fails to link an app using exp2/pow/etc. functions from libm when -ffast-math is used and optimizations are turned off (-O0, the default). This applies to both clang-9 and clang-10; gcc doesn't suffer from this issue.

Version-Release number of selected component (if applicable):
clang-9.0.0-1.fc31 or clang-10.0.0-0.1.rc1.fc32
glibc-2.31-1.fc32

How reproducible:
always

Steps to Reproduce:
$ cat > test.c << EOF
#include <stdio.h>
#include <math.h>

int main(void) {
	printf("Hello %lf, %lf\n", exp2(2.0), pow(2.0, 3.0));
	return 0;
}
EOF

$ clang -o test test.c -lm -ffast-math

Actual results:
## Without optimizations (clang-9)
$ clang -o test test.c -lm -ffast-math
/usr/bin/ld: /tmp/test-0dc25f.o: in function `main':
test.c:(.text+0x18): undefined reference to `__exp2_finite'
/usr/bin/ld: test.c:(.text+0x38): undefined reference to `__pow_finite'
clang-9: error: linker command failed with exit code 1 (use -v to see invocation)

## Without optimizations (clang-10)
$ clang -o test test.c -lm -ffast-math 
/usr/bin/ld: /tmp/test-e3abbe.o: in function `main':
test.c:(.text+0x18): undefined reference to `__exp2_finite'
/usr/bin/ld: test.c:(.text+0x38): undefined reference to `__pow_finite'
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)

## With optimizations (-O1 and higher, both clang-9 and clang-10)
$ clang -o test test.c -lm -ffast-math -O1
$ echo $?
0
$ ./test 
Hello 4.000000, 8.000000

Expected results:
Compilation should succeed.

## Without optimizations (gcc-10)
$ gcc -o test test.c -lm -ffast-math
$ echo $?
0
$  ./test 
Hello 4.000000, 8.000000

Additional info:
The issue is not present with glibc-2.30-5.fc31. The same issue appears on Arch Linux with clang-9 and glibc-2.31-1.

## clang-10 verbose output
$  clang -o test test.c -lm -ffast-math -v
clang version 10.0.0 (Fedora 10.0.0-0.1.rc1.fc32)
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /usr/bin
Found candidate GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/9
Found candidate GCC installation: /usr/lib/gcc/x86_64-redhat-linux/9
Selected GCC installation: /usr/bin/../lib/gcc/x86_64-redhat-linux/9
Candidate multilib: .;@m64
Candidate multilib: 32;@m32
Selected multilib: .;@m64
 (in-process)
 "/usr/bin/clang-10" -cc1 -triple x86_64-unknown-linux-gnu -emit-obj -mrelax-all -disable-free -disable-llvm-verifier -discard-value-names -main-file-name test.c -mrelocation-model static -mthread-model posix -mframe-pointer=all -menable-no-infs -menable-no-nans -menable-unsafe-fp-math -fno-signed-zeros -mreassociate -freciprocal-math -ffp-contract=fast -fno-rounding-math -ffast-math -ffinite-math-only -masm-verbose -mconstructor-aliases -munwind-tables -target-cpu x86-64 -dwarf-column-info -fno-split-dwarf-inlining -debugger-tuning=gdb -v -resource-dir /usr/lib64/clang/10.0.0 -internal-isystem /usr/local/include -internal-isystem /usr/lib64/clang/10.0.0/include -internal-externc-isystem /include -internal-externc-isystem /usr/include -fdebug-compilation-dir / -ferror-limit 19 -fmessage-length 0 -fgnuc-version=4.2.1 -fobjc-runtime=gcc -fdiagnostics-show-option -fcolor-diagnostics -faddrsig -o /tmp/test-5d05c7.o -x c test.c
clang -cc1 version 10.0.0 based upon LLVM 10.0.0 default target x86_64-unknown-linux-gnu
ignoring nonexistent directory "/include"
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/include
 /usr/lib64/clang/10.0.0/include
 /usr/include
End of search list.
 "/usr/bin/ld" --hash-style=gnu --build-id --eh-frame-hdr -m elf_x86_64 -dynamic-linker /lib64/ld-linux-x86-64.so.2 -o test /usr/bin/../lib/gcc/x86_64-redhat-linux/9/../../../../lib64/crt1.o /usr/bin/../lib/gcc/x86_64-redhat-linux/9/../../../../lib64/crti.o /usr/bin/../lib/gcc/x86_64-redhat-linux/9/crtbegin.o /usr/bin/../lib/gcc/x86_64-redhat-linux/9/crtfastmath.o -L/usr/bin/../lib/gcc/x86_64-redhat-linux/9 -L/usr/bin/../lib/gcc/x86_64-redhat-linux/9/../../../../lib64 -L/usr/bin/../lib64 -L/lib/../lib64 -L/usr/lib/../lib64 -L/usr/bin/../lib/gcc/x86_64-redhat-linux/9/../../.. -L/usr/bin/../lib -L/lib -L/usr/lib /tmp/test-5d05c7.o -lm -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/bin/../lib/gcc/x86_64-redhat-linux/9/crtend.o /usr/bin/../lib/gcc/x86_64-redhat-linux/9/../../../../lib64/crtn.o
/usr/bin/ld: /tmp/test-5d05c7.o: in function `main':
test.c:(.text+0x18): undefined reference to `__exp2_finite'
/usr/bin/ld: test.c:(.text+0x38): undefined reference to `__pow_finite'
clang-10: error: linker command failed with exit code 1 (use -v to see invocation)