x11/pixman: fix build on armv7

• due to a regression in some binutils>2.40 version, the assembly code no longer assembles. Remove leading zeros from local labels to fix this.
• the arm64 assembly code has some other issue which appears to have been fixed upstream in 0.43.0, so don't bother with that; PR 276296 will address this.

See also: https://gitlab.freedesktop.org/pixman/pixman/-/issues/96
MFH: 2024Q4