GCC fails to recognize constants as immediates for SIMD intrinsics such as `_mm_srli_si128` when using a precompiled header (PCH) built from a header that temporarily applies `#pragma GCC optimize("Og")` inside `#pragma GCC push_options` / `#pragma GCC pop_options`.

This is not a case where the PCH is built and used with different command-line optimization flags. The command-line flags match. The only optimization change is the scoped pragma inside the header, and that state is restored before the end of the header.

Minimal source files:

`pch.hxx`
```cpp
#pragma GCC push_options
#pragma GCC optimize("Og")
#include <bits/c++config.h>
#pragma GCC pop_options
```

`repro.cpp`
```cpp
#include <emmintrin.h>

void f() {
  __m128i x = _mm_setzero_si128();
  x = _mm_srli_si128(x, 2);
}
```

Reproducible: Always

Steps to Reproduce:
g++ -x c++-header -std=c++20 -g -Winvalid-pch \
  -include ./pch.hxx \
  -o ./pch.hxx.gch \
  -c pch.hxx.cxx

g++ -std=c++20 -g -Winvalid-pch \
  -include ./pch.hxx \
  -c repro.cpp

# control: same source without PCH
g++ -std=c++20 -g -c repro.cpp
Actual Results:
In function ‘__m128i _mm_srli_si128(__m128i, int)’,
    inlined from ‘void f()’ at repro.cpp:5:20:
/usr/lib/gcc/.../include/emmintrin.h:1230:10: error: the last argument must be an 8-bit immediate

Expected Results:
Compilation should succeed. The literal `2` should be recognized as an immediate. The same `repro.cpp` compiles successfully without PCH.

Additional Information:
- The reproducer uses the same command-line flags for PCH creation and use: `-std=c++20 -g`.
- The same `repro.cpp` compiles successfully without PCH.
- `emmintrin.h` changes some intrinsic definitions based on `__OPTIMIZE__`, so this appears related to pragma-driven optimization state during PCH save/load.
- This can be triggered by common libraries such as `fmt`, but the attached reproducer is non-`fmt`, so `fmt` is only one trigger path.
- Maybe related to PR c++/48026 (early pragma handling), but the issue still reproduces with GCC 16.0.1 on Fedora Rawhide.

Fedora 43 / GCC 15.2.1:

```bash
$ g++ -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,cobol,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugzilla.redhat.com/ --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-libstdcxx-backtrace --with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-15.2.1-build/gcc-15.2.1-20260123/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none,amdgcn-amdhsa --enable-offload-defaulted --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux --with-build-config=bootstrap-lto --enable-link-serialization=1 --disable-libssp
Thread model: posix
gcc version 15.2.1 20260123 (Red Hat 15.2.1-7) (GCC)
$ cat /etc/fedora-release
Fedora release 43 (Forty Three)
$ rpm -qa | grep -E "^(gcc|fmt)-[0-9].*x86_64"
fmt-11.2.0-3.fc43.x86_64
gcc-15.2.1-7.fc43.x86_64
```

Fedora Rawhide / GCC 16.0.1:

```bash
$ g++ -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --enable-bootstrap --enable-languages=c,c++,fortran,objc,obj-c++,ada,go,d,m2,cobol,algol68,lto --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=https://bugzilla.redhat.com/ --enable-shared --enable-threads=posix --enable-checking=release --enable-multilib --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-linker-build-id --with-gcc-major-version-only --enable-libstdcxx-backtrace --with-libstdcxx-zoneinfo=/usr/share/zoneinfo --with-linker-hash-style=gnu --enable-plugin --enable-initfini-array --with-isl=/builddir/build/BUILD/gcc-16.0.1-build/gcc-16.0.1-20260321/obj-x86_64-redhat-linux/isl-install --enable-offload-targets=nvptx-none,amdgcn-amdhsa --enable-offload-defaulted --without-cuda-driver --enable-gnu-indirect-function --enable-cet --with-tune=generic --with-tls=gnu2 --with-arch_32=i686 --build=x86_64-redhat-linux --with-build-config=bootstrap-lto --enable-link-serialization=1 --disable-libssp
Thread model: posix
gcc version 16.0.1 20260321 (Red Hat 16.0.1-0) (GCC)
$ cat /etc/fedora-release
Fedora release 45 (Rawhide)
$ rpm -qa | grep -E "^gcc-[0-9].*x86_64"
gcc-16.0.1-0.10.fc45.x86_64
```