master branch: commit r15-4191 failed to bootstrap on Linux/x86_64 (commit r15-4186 builds)!

[haochenj@gnu-skx-1.sc.intel.com]

make[2]: Entering directory '/export/home/haochenj/src/gcc-regression'
rm -rf bld
mkdir -p bld
cd bld; \
RUNTESTFLAGS="--target_board='unix{-m32,}'" ../src-master/configure \
	--with-arch=corei7 --with-cpu=corei7 --enable-clocale=gnu --with-system-zlib --enable-shared --enable-cet --with-demangler-in-ld --enable-libmpx --prefix=/usr/gcc-15.0.0 --with-fpmath=sse 
checking build system type... x86_64-pc-linux-gnu
    grep -E "(error:|Error)" makelog.r15-4191.x86_64.corei7 >> makelog.r15-4191.x86_64.corei7.mail; \
    tail -n +20 makelog.r15-4191.x86_64.corei7 | grep -C 10 -E "error:|Error:" >> makelog.r15-4191.x86_64.corei7.mail; \
make[6]: [Makefile:1832: x86_64-pc-linux-gnu/bits/largefile-config.h] Error 1 (ignored)
make[6]: [Makefile:1831: x86_64-pc-linux-gnu/bits/largefile-config.h] Error 1 (ignored)
make[6]: [Makefile:1832: x86_64-pc-linux-gnu/bits/largefile-config.h] Error 1 (ignored)
../../src-master/libcpp/directives.cc:2078:20: error: unknown conversion type character ‘<’ in format [-Werror=format=]
../../src-master/libcpp/directives.cc:2078:34: error: unknown conversion type character ‘>’ in format [-Werror=format=]
make[6]: *** [Makefile:227: directives.o] Error 1
make[5]: *** [Makefile:12975: all-stage2-libcpp] Error 2
make[4]: *** [Makefile:30028: stage2-bubble] Error 2
make[3]: *** [Makefile:30272: bootstrap] Error 2
make[2]: *** [Makefile:313: bootstrap] Error 2
==================== Detailed Info around error (+- 10 Lines) ====================
checking for x86_64-pc-linux-gnu-objdump... objdump
checking how to recognize dependent libraries... pass_all
checking for x86_64-pc-linux-gnu-dlltool... dlltool
checking how to associate runtime and link libraries... printf %s\n
checking for x86_64-pc-linux-gnu-ar... (cached) ar --plugin /usr/libexec/gcc/x86_64-redhat-linux/14/liblto_plugin.so
checking for archiver @FILE support... @
checking for x86_64-pc-linux-gnu-strip... no
checking for strip... strip
checking for x86_64-pc-linux-gnu-ranlib... ranlib --plugin /usr/libexec/gcc/x86_64-redhat-linux/14/liblto_plugin.so
checking command to parse nm output from  /export/home/haochenj/src/gcc-regression/bld/./prev-gcc/xgcc -B/export/home/haochenj/src/gcc-regression/bld/./prev-gcc/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/bin/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/bin/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/lib/ -isystem /usr/gcc-15.0.0/x86_64-pc-linux-gnu/include -isystem /usr/gcc-15.0.0/x86_64-pc-linux-gnu/sys-include   -fno-checking object... ../../src-master/libcpp/directives.cc: In function ‘void do_pragma_once(cpp_reader*)’:
../../src-master/libcpp/directives.cc:2078:20: error: unknown conversion type character ‘<’ in format [-Werror=format=]
 2078 |                  "%<#pragma once%> in main file");
      |                    ^
../../src-master/libcpp/directives.cc:2078:34: error: unknown conversion type character ‘>’ in format [-Werror=format=]
 2078 |                  "%<#pragma once%> in main file");
      |                                  ^
ok
checking for sysroot... no
checking for a working dd... /bin/dd
checking how to truncate binary pipes... /bin/dd bs=4096 count=1
checking for x86_64-pc-linux-gnu-mt... no
checking for mt... no
checking if : is a manifest tool... no
checking how to run the C preprocessor...  /export/home/haochenj/src/gcc-regression/bld/./prev-gcc/xgcc -B/export/home/haochenj/src/gcc-regression/bld/./prev-gcc/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/bin/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/bin/ -B/usr/gcc-15.0.0/x86_64-pc-linux-gnu/lib/ -isystem /usr/gcc-15.0.0/x86_64-pc-linux-gnu/include -isystem /usr/gcc-15.0.0/x86_64-pc-linux-gnu/sys-include   -fno-checking -E