Strip GCC-only -fno-merge-constants from flags in conda build (#2978)

conda-forge's `gcc`/`g++` compiler activation injects
`-fno-merge-constants` into `CFLAGS`/`CXXFLAGS` when `CONDA_BUILD==1`.

The dpnp conda recipe builds with the Intel oneAPI compilers
(`icx`/`icpx`), which do not implement this GCC flag and emit a warning
on every compile unit:
```
icpx: command line warning #10430: Unsupported command line options encountered
These options as listed are not supported.
For more information, use '-qnextgen-diag'.
option list:
-fno-merge-constants
```

This PR removes `-fno-merge-constants` from `CFLAGS`/`CXXFLAGS` in
`conda-recipe/build.sh`. f60cdfe

Author: github-actions[bot]

reference/comparison.html

@@ -1040,7 +1040,7 @@
 <h1>Comparison Table NumPy/ DPNP/ CuPy<a class="headerlink" href="#comparison-table-numpy-dpnp-cupy" title="Link to this heading">¶</a></h1>
 <p>Here is a list of NumPy and CuPy APIs and its corresponding DPNP implementations.</p>
 <p><code class="docutils literal notranslate"><span class="pre">-</span></code> in DPNP column means that DPNP implementation is not provided yet.</p>
-<p><strong>NumPy(v2.5.0) / DPNP(v0.21.0dev2+6.gf9ae57627bc) / CuPy(v14.1.1) APIs</strong></p>
+<p><strong>NumPy(v2.5.0) / DPNP(v0.21.0dev2+7.gf60cdfe6c72) / CuPy(v14.1.1) APIs</strong></p>
 <section id="summary">
 <h2>Summary<a class="headerlink" href="#summary" title="Link to this heading">¶</a></h2>
 <div class="table-wrapper docutils container">