nir: rename nir_lower_samplers.c{pp,}

With the only C++ function having its own wrapper we can 'demote' this
file to a normal C one. This allows us to get rid of extern C { #include
<foo.h> } 'hacks'. Plus some of the headers may use C99 initializers,
which are not supported by the ISO standard.

This may cause build issue on incremental builds. If so run the
following:

sed -i -e 's|samplers\.cpp|samplers.c|' src/glsl/nir/.deps/nir_lower_samplers.Plo

Fixes: ef8eebc6ad5(nir: support indirect indexing samplers in struct arrays)
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reported-by: Gottfried Haider <gottfried.haider@gmail.com>
Tested-by: Gottfried Haider <gottfried.haider@gmail.com>
Reviewed-by: Timothy Arceri <t_arceri@yahoo.com.au>

src/glsl/Makefile.sources

@@ -43,7 +43,7 @@ NIR_FILES = \
 	nir/nir_lower_io.c \
 	nir/nir_lower_outputs_to_temporaries.c \
 	nir/nir_lower_phis_to_scalar.c \
-	nir/nir_lower_samplers.cpp \
+	nir/nir_lower_samplers.c \
 	nir/nir_lower_system_values.c \
 	nir/nir_lower_tex.c \
 	nir/nir_lower_to_source_mods.c \

src/glsl/nir/nir_lower_samplers.c

@@ -29,12 +29,10 @@
 #include "program/hash_table.h"
 #include "ir_uniform.h"
 
-extern "C" {
 #include "main/compiler.h"
 #include "main/mtypes.h"
 #include "program/prog_parameter.h"
 #include "program/program.h"
-}
 
 /* Calculate the sampler index based on array indicies and also
  * calculate the base uniform location for struct members.
@@ -78,7 +76,7 @@ calc_sampler_offsets(nir_deref *tail, nir_tex_instr *instr,
 
    case nir_deref_type_struct: {
       nir_deref_struct *deref_struct = nir_deref_as_struct(tail->child);
-      *location += tail->type->record_location_offset(deref_struct->index);
+      *location += glsl_get_record_location_offset(tail->type, deref_struct->index);
       calc_sampler_offsets(tail->child, instr, array_elements,
                            indirect, b, location);
       break;
@@ -179,7 +177,7 @@ lower_impl(nir_function_impl *impl, const struct gl_shader_program *shader_progr
    nir_foreach_block(impl, lower_block_cb, &state);
 }
 
-extern "C" void
+void
 nir_lower_samplers(nir_shader *shader,
                    const struct gl_shader_program *shader_program)
 {