Pass -fpch-preprocess to GCC when precompiled headers are used

CCache requires this flag when building with precompiled headers.
Without it, the preprocessor fails and CCache fallbacks to running the
real compiler.

Users still need to set 'sloppiness' to 'pch_defines,time_macros' in
their ccache.conf file for CCache to cache builds that use precompiled
headers. See the CCache manual for more info:

	https://ccache.samba.org/manual.html#_precompiled_headers

1 files changed, 5 insertions, 0 deletions

diff --git a/mesonbuild/compilers/cpp.py b/mesonbuild/compilers/cpp.py
index a933f0e..a9093b3 100644
--- a/mesonbuild/compilers/cpp.py
+++ b/mesonbuild/compilers/cpp.py
@@ -12,6 +12,8 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import os.path
+
 from .. import coredata
 from ..mesonlib import version_compare
 
@@ -126,6 +128,9 @@ class GnuCPPCompiler(GnuCompiler, CPPCompiler):
             return options['cpp_winlibs'].value[:]
         return []
 
+    def get_pch_use_args(self, pch_dir, header):
+        return ['-fpch-preprocess', '-include', os.path.split(header)[-1]]
+
 
 class IntelCPPCompiler(IntelCompiler, CPPCompiler):
     def __init__(self, exelist, version, icc_type, is_cross, exe_wrap):